1/5 I \

Le ngoc Sen

INFLUENCE OF VARIOUS WATER MANAGEMENT AND AGRONOMIC PACKAGES ON THE

CHEMICAL CHANGES AND ON THE GROWTH OF RICE IN ACID SULPHATE SOILS

Proefschrift

ter verkrijging van de graad van

doctor in de landbouwwetenschappen

op gezag van de rector magnificus,

Dr. C.C. Oosterlee,

in het openbaar te verdedigen

op dinsdag 19 april 1988

des namiddags te vier uur in de aula

van de Landbouwuniversiteit te Wageningen

CENTRALE LANDBOUWCATALOGUS

0000 0212 9738

/SAJ ̂ 2 6& / ^ 7 tyiC/^i

Promotoren: Prof.Dr.Ir. W.H. van der Molen, emiritus hoogleraar in de

agrohydrologie

Prof.Dr.Ir. L.J. Pons, emeritus hoogleraar in de regionale

bodemkunde

fJ,jo22ot,>*-

Statements

1. Up to now, undisturbed lysimeters (soil columns) for the study of

water and solute movement in the soil have been underused in re­

search on soils and especially in acid sulphate soils.

2. Mulching the surface soil of acid sulphate soils during the dry

season is a good measure to avoid the accumulation of toxic ele­

ments in the surface soil.

3. Research on problem soils without site characterization has limited

application.

4. Reclamation of problem soils without proper identification of

the soil properties is apt to be disappointing.

5. Agricultural research in developing countries should aim at raising

the poor farmers' standard of living.

6. Small scale development does not produce large errors.

7. Poor farmers often do not benefit from high technology.

8. Correction of errors and mistakes will be impeded if the real

causes of mistakes are not exposed.

9. Higher scientific degrees help the holder to acquire recognition

and social status. It is not, however, a good yardstick to measure

ability in practice.

10. In the Far-East, people distinguish a degree holder from a learned

man, and the latter from a talented man. It is a good way of judging

scientists.

11. F. Engels wrote: "Nature will avenge itself on our thoughtless

acts if we do not act in conformity with its laws". In line with

that statement one can say that it is necessary to take measures in

preserving ecology as soon as possible, otherwise our ecosystem

will further be destabilized.

Frederick Engels, 187S-1876

Acknowledgements

The author wishes to thank Prof.Dr.Ir. L.J. Pons and Prof.Dr.Ir.

W.H. van der Molen, whose interest and guidance during the study and

the preparation of the manuscript were invaluable. The great contribu­

tion of Prof.Dr. N. van Breemen and Dr. R. Brinkman in the initiation

and the execution of the study is very much appreciated.

The author also wishes to thank the following:

Dr. T. Wickham, former head Irrigation and Water Management Depart­

ment of The International Rice Reseach Institute for his help and

encouragement.

- Dr. S.I. Bhuiyan, head Irrigation and Water Management Department of

the International Rice Research Institute for his many invaluable

help.

- Dr. F.N. Ponnamperuma, head Soil Chemistry Department of the Inter­

national Rice Research Institute for generous help in many ways.

- Dr. H. van Keulen of CABO for his cooperation in the development of

the simulation model.

- Mr. G. van Hoof of the Computer Center, Wageningen Agricultural

University, for his unselfish assistance whenever needed.

- Staff members of Irrigation Water Management Department and Soil

Chemistry Department of the International Rice Research Institute.

Staff members of Soil Sciences and Geology Department Wageningen

Agricultural University for their help.

Staff members of Analytical Service Laboratory of the International

Rice Research Institute for the analytical work.

Mrs. Th. Neijenhuis and Mrs. E. Olofsen of the Central typing office

of the Wageningen University.

Those friends whom I cannot ennumerate here.

Finally, the author would like to dedicate this piece of work to his

parents, whose sacrify their whole lives for the welfare of their

children, and to his wife and his son, who share his many burdens in

life. The research was sponsored by the International Rice Research

Institute, the Interim Mekong Committee and the Dutch Technical Cooper­

ation program.

CONTENTS page

1 INTRODUCTION 1

2 INFLUENCE OF VARIOUS WATER MANAGEMENT AND AGRONOMIC

PACKAGES ON THE CHEMICAL CHANGES AND ON THE GROWTH

OF RICE IN ACID SULPHATE SOILS 4

2.1 Background of research on acid sulphate soils 5

2.1.1 Acid sulphate soils and their distribution 5

2.1.2 Causes of low productivity 6

2.1.3 Reclamation and improvement 11

2.1.4 The needs for research to monitor chemical

changes and plant performance under various

reclamation measures 14

2.2 Materials and methods 15

2.2.1 Preparation of undisturbed soil cores 15

2.2.2 Experimental treatments 20

2.2.3 Analytical methods 24

2.3 Results and discussion 25

2.3.1 The amount of drainage water collected under

different water management practices during

the first and second leaching periods 25

2.3.2 Average soil moisture content (by weight)

and n-value of different depths of Aparri

and Sinacaban soils at the end of dry season 27

2.3.3 Chemical properties of the soil solution of

Aparri and Sinacaban acid sulphate soils

during first leaching period and first crop 27

2.3.3.1 Aparri soil 27

2.3.3.2 Sinacaban soil 30

2.3.4 Chemical properties of the soil solutions

of Aparri and Sinacaban acid sulphate soils

during second leaching period, second and

third rice crops 30

2.3.4.1 Aparri soil 30

2.3.4.2 Sinacaban soil 32

2.3.5 Effects of water management and agronomic

packages on the grain yield of rice in

two acid sulphate soils 55

2.3.5.1 Aparri acid sulphate soil 56

2.3.5.2 Sinacaban acid sulphate soil 58

2.4 Summary and conclusions 65

2.5 References 67

Appendix 2.1 76

EVAPORATION AND ACIDIFICATION PROCESSES IN AN ACID

SULPHATE SOIL 79

3.1 Introduction 80

3.2 Materials and methods 80

3.3 Results and discussion 85

3.3.1 Evaporation 85

3.3.2 Sulphur fraction 86

3.3.3 The distribution of pH, total acidity,

non acid cations and soil moisture in

different soil colums 86

3.3.4 Total acidity 91

3.3.5 Basic cations 92

3.3.6 Soil moisture 92

3.3.7 Changes of pH and total acidity of water

extracts with cumulative evaporation 93

3.3.8 General results and discussion 95

3.4 References 97

EFFECTS OF ACID SULPHATE FLOOD WATER ON THE CHEMICAL

CHANGES AND GROWTH OF RICE IN ACID SULPHATE SOILS 99

4.1 Introduction 100

4.2 Materials and methods 102

4.3 Results and discussion 103

4.3.1 Effects of acid sulphate floodwater on the

chemical changes of acid sulphate soils

during the early growth period of rice 103

4.3.1.1 Effect of pH of floodwater 103

4.3.1.2 Effects of iron concentration in

acid sulphate floodwater 107

4.3.1.3 Effects of aluminium in acid sulphate

floodwater 111

4.3.2 Effects of acid sulphate flood water on

plant dry matter yield and chemical com­

positions of IR36 on three acid sulphate

soils for two seasons 115

4.3.3 Quantitative relationship between acid

sulphate flood water and plant dry

matter yield 122

4.3.2.1 First crop 115

4.3.2.2 Second crop 120

4.4 Conclusions 122

4.5 References 124

THE EFFECTIVENESS OF ROCK PHOSPHATES FOR LOWLAND

RICE ON ACID SULPHATE SOILS UNDER VARIOUS MANAGEMENT

PRACTICES 125

5.1 Introduction 125

5.2 Objective 126

5.3 Materials and methods 127

5.4 Results and discussion 128

5.4.1 Effect of variation in phosphate rate, time

of fertilizer application and soil moisture

status on pH of the soil solution at trans­

planting and at 6 weeks after transplanting 128

5.4.2 Effect of variation in phosphate rate, time

of fertilizer application and soil moisture

status on grain yield, straw weight, plant

height, tiller and panicle numbers 130

5.4.3 Effect of variation in phosphate rate, time

of fertilizer application and soil moisture

status on the chemical composition of rice

plants during the growing period 132

5.4.4 Relative agronomie effectiveness of rock

phosphate compared with super phosphate 132

5.5 Conclusions and recommendations 135

5.6 References 137

6 SIMULATION OF OXIDATION AND ACIDIFICATION PROCESSES

IN ACID SULPHATE SOILS 139

6.1 Introduction 140

6.2 Oxidation process in acid sulphate soils 141

6.3 Computer simulation of the oxidation process 145

6.4 Water movement section 147

6.5 Flow of oxygen in the profile 154

6.5.1 The diffusion coefficient of oxygen in

an aggregate, DCSPH 158

6.5.2 The relative solubility of oxygen in water,

SOLO 159

6.5.3 The critical concentration of oxygen, CCO 159

6.5.4 The diffusion coefficient of oxygen in

free air, DZERO 159

6.5.5 The ratio D/DO for soil air 159

6.5.6 Oxygen consumption, RCOX 160

6.5.7 The sulphate production, (PSO.) and

acid production, RHYD 160

6.6 Transport of cations in the soil profile 161

6.7 Calculation of the composition of the exchange

complex and the soil solution for five cations 162

6.8 Calculation cation transport in the soil profile 165

6.9 Results and discussion 167

6.10 References 175

Appendix 6.1 180

Appendix 6.2 198

7 SUMMARY 202

INTRODUCTION

Acid sulphate soils are derived from marine and estuarine sediments

containing high concentrations of reduced sulphur components. Upon

drainage and aeration they show a definite and severe acidification due

to the oxidation of sulphides (mainly pyrites, FeS ) leading to the

formation of sulphuric acid. These soils have pH values below 3.5 (if

Entisols) or 4 (if Inceptisols) in the upper 50 cm. They are found both

in the temperate and tropical regions, but the vast majority of such

soils are in the economically underdeveloped tropics where mounting

population pressure will require maximum utilization of all available

land in the near future.

About 13 million hectares of potential agricultural lands in tidal

swamp areas are not developed because of acid sulphate soils

(Table 1.1). There are about 5 million hectares of these soils in

south and southeast Asia, about 3.7 million hectares in Africa and

about 2 million hectares in south America (van Breemen, 1980).

Although physiographic and hydrologie conditions are generally favour­

able for rice growing in acid sulphate soils, a number of unfavourable

factors such as soil acidity, salinity, aluminium toxicity, iron tox­

icity, hydrogen sulphide concentration and nutrient deficiencies as­

sociated with high acidity, preclude efficient utilization of such

land.

The high degree of acidity (or potential acidity) of acid sulphate

soils makes reclamation through liming economically impractical in most

cases. The only practical way to manage these soils is by proper drain­

age and water management. Maintaining a high water table can control

Table 1.1 World distribution of acid sulphate soils (millions ha).

Tt

Asia and Far East

Africa

Latin America

North America

Other regions

World total

Length of

< 90

0.0

0.4

0.0

0.0

-

0.4

growing pe

90-180

0.2

0.7

0.1

0.0

-

1.1

180-

5.1

1.5

0.8

0.0

-

7.4

riods

300

(days)

> 300

1.4

1.1

1.2

0.0

-

3.7

total

6.7

3.7

2.1

0.1

0.0

12.6

Adapted from Beek et al. (1980), based on data from FAO/UNESCO soil

map of the world. Growing period data according to FAO Agro- ecolog­

ical zone project, Rome

the oxidation of pyrite (the sulfur source in these soils). Where fea­

sible, drainage and removal of acidity by leaching can be used. Proper

water management and drainage control have made rice production pos­

sible in large acid sulphate areas of Thailand and Vietnam.

This thesis is the outcome of various studies. In Chapter 2 an inves­

tigation about the influence of different water management and agron­

omic packages on the chemical changes and on the growth of rice in acid

sulphate soil is given. A simple, low-cost lysimeter was developed to

investigate the above objectives. Various methods of water managements

and agronomic practices will be pointed out.

Chapter 3 describes soil column experiments carried out to study the

evaporation and acidification process in acid sulphate soil.

Chapter 4 deals with the effects of acid sulphate flood water on the

chemical changes and on the growth of rice in acid sulphate soils.

Chapter 5 presents results of pot experiments on the effect of differ­

ent methods of application of rock phosphate fertilizers on the trans­

formation of phosphorus in acid sulphate soils.

Chapter 6 gives a simulation of the oxidation and acidification proces­

ses in acid sulphate soils.

Chapter 7 contains the conclusions and recommendations for future re­

search.

References

Beek, K.J., W.A. Blokhuis, P. Driessen, N. van Breemen, R. Brinkman

and L.J. Pons, 1980. Problem soils: their reclamation and management.

In: ILRI Publ. no. 27: 43-72.

Breemen, N. van, 1980. Acidity of wetland soils, including Histosols

as a constraint to food production. In: Priorities for alleviating

soil related constraint to food production in the tropics. Inter­

national Rice Research Institute and New York State College of

Agriculture and Life Sciences, Cornell University, pp. 189-202.

INFLUENCE OF VARIOUS WATER MANAGEMENT AND AGRONOMIC PACK­

AGES ON THE CHEMICAL CHANGES AND ON THE GROWTH OF RICE IN

ACID SULPHATE SOILS

Abstract

Forty undisturbed soil cores of two acid sulphate soils (60 cm dia­

meter, 90 cm deep) in the Philippines were used to study the influence

of drainage, liming, percolation and mulching on the growth of IR 36

rice cultivar and on the chemical changes during two leaching periods

and three cropping seasons. Grain yields differed greatly among the two

soils and three cropping seasons. In Aparri soil, there were no marked

effect of drainage, liming and agronomic practices on grain yield over

three cropping seasons. This was associated with high pH in the surface

soil and minimal pyrite oxidation in the subsoil. In Sinacaban soil,

during the first season, grain yields were hardly affected by treat­

ments because the soils did not undergo drying and oxidation. During

the second and third season, the influence of different treatments on

grain yields was very pronounced. Deep drainage treatment gave the

poorest yields in both second and third crops. Highest yields were ob­

tained in the surface flushing treatment, the next highest yields with

shallow drainage. Contrary to expectation, the grain yield in deep

drainage treatments was lower with, than without percolation at ap­

plication of 2.5 tons of lime/ha. Mulching increased grain yield by 67

and 30 percent for the second and third crops, respectively. In the

deep drainage treatment, only a high amount of lime, 2.5 tons/ha,

produced a yield exceeding the equivalent of about 1 t/ha. The frequen­

cy of occurrence of successful crops under different practices revealed

the superiority of the flushing treatment. The concept of average min-

eral stress index (AMSI) was introduced as a measure for toxic elements 2+ 3+

in acid sulphate soils (pH, Fe and Al ) . This index gave certain

indications of grain yield: below AMSI = 40 reasonable yields were ob­

tained, above AMSI = 100 the crop failed completely.

The chemical changes of different treatments were monitored during the

two leaching periods and during the growing seasons for different

depths along the soil profile and for the surface water. The chemical

changes varied with soil and management practices. Deep drainage in

Sinacaban soil produced a large amount of acidity, and the frequency of

occurrence of pH less than 3.5 was 100 percent for layers below 40 cm

depth. Shallow drainage treatment did not cause severe oxidation in the

subsoil layers and produced less acidity. The reduction process fol­

lowed the same trend with other experiments for surface soil. Even with

prolonged submergence, reduction took place very slowly in the subsoil

layers. Acidity remained very high for a long period (9 months). In

addition to the high acidity, iron (II) was also very high, which ham­

pered the growth of rice. Concentration of aluminium decreased as the

pH of the soil increased. Minimizing pyrite oxidation is therefore

recommended to avoid the adverse effects of toxic elements.

2.1 Background of research on acid sulphate soils

2.1.1 Acid sulphate soils and their distribution

Acid sulphate soils are usually derived from marine and estuarine sedi­

ments containing high concentrations of reduced sulphur compounds. They

show a definite and severe acidification upon drainage and aeration,

owing to the oxidation of sulphides (mainly pyrites, FeS„) , with for­

mation of sulphuric acid. They are found both in the temperate and

tropical regions, but the vast majority in the tropics (Kawalec, 1973).

They cover more than 15 million hectares of flat land well suited to

year-long rice growing. Because of the high acidity and large amounts

of toxic substances in the soil, they are left uncultivated or put

only to marginal use. Farmers have devised means of farming part of

these soils for lowland rice but generally obtain very low returns.

2.1.2 Causes of low productivity

The low productivity of acid sulphate soils may be due to one or more

of the following unfavourable factors: soil acidity, salinity, alumi­

nium toxicity, iron toxicity and low nutrient status.

Soil acidity

Soil acidity per se is harmful to plants and impairs the absorption of

nutrients, especially of calcium and phosphorus (Arnon and Johnson,

1942, Arnon et al., 1942). Rorison (1973) pointed out that plants may

tolerate relatively large concentrations of H ions, as long as the

concentrations of other cations are large, and the concentration of

toxic polyvalent cations is small. Rice in its vegatative growth stage

was found not to be affected by H concentrations up to pH 3.5, al­

though the high acidity suppressed the uptake of metallic cations

(Thawornwong and van Diest, 1974). A low pH aggravates the harmful ef­

fects of organic acids (Tanaka and Navasero, 1967). Low pH inhibits the

conversion of ammonium to nitrate, so that NH4 ions accumulate. Some

plants take up both ammonium and nitrate ions, but calcicole species

may give poor or no growth when supplied with NH.-N at pH 4.2 whereas

calcifuge plants flourish with NH.-N at that pH (Rorison, 1973).

Salinity

There are large increases in soluble salts when pyritic soils are

drained and oxidized. Ponnamperuma et al. (1973) report specific con­

ductance levels exceeding 10 mS/cm in some acid sulphate soils.

Rice is a moderately salt tolerant crop (Richards, 1954). It is very

tolerant during germination but sensitive at the 1-2 leaf stage. The

tolerance of rice progressively increases during the tillering and

elongation stages of development and again decreases at the time of

floret fertilization. Excess salt retards growth and depresses yield

(Iwaki et al., 1953; Iwaki, 1956; Pearson, 1961). Zashariah and Sanka-

rasubramoney (1961) found that the salt tolerance of all varietites of

paddy increases with maturity. Sprouted rice seed grew normally in a

culture solution when the specific conductivity was less than 4 mS/cm.

Between 4 and 11 mS/cm, growth was retarded, and at a conductivity

greater than 11 mS/cm the seedling failed to grow (Pearson, 1959).

These results were confirmed by IRRI (1967).

Aluminium toxicity

Aluminium is normally the major exchangeable cation in very acid soils.

It becomes more soluble at low pH. The relationship between pH and Al

concentration in a soil solution is given as:

pAl = 2pH - 4.41 (Mai thi My Nhung and Fonnamperuma, 1966).

In various crops (Nagata, 1953; Nomoto and Kisida, 1959) including rice

(Cate and Sukhai, 1964), aluminium toxicity is first evidenced by root

injury (coralloid stunted roots) and then by characteristic symptoms on

the leaves.

Aluminium toxicity is reportedly due to the inactivation of phosphorus,

especially in the roots (Wright, 1943) and also to the coagulation of

proteins (Aimi and Murakami, 1964).

The critical concentrations of Al in solution and the critical contents

of Al in plants vary for different species. Aluminium toxicity to rice

was first reported by Miyake in 1916, who showed that 1.2 mg Al/1 in

solution was toxic. Cate and Sukhai (1964) stated that in the temporary

absence of nutrient cations, 1 to 2 mg/1 of soluble Al markedly inhib­

its the growth of rice roots. Tanaka and Navasero (1966) considered

30 mg Al/1 in rice shoots as a critical value. Above this level, Al-

toxicity symptoms often developed. The deleterious effect of Al on the

growth of rice was especially noticeable in the seedling stage (Tha-

wornwong and van Diest, 1974). A concentration of 2 mg Al/1, either in

chloride or in chelate form did not affect the growth of rice when ap­

plied after the seedling stage (Thawornwong and van Diest, 1974).

The critical value was found to vary with the P status of the plant,

and with the Fe concentration and pH in the culture solution. Liming a

low-pH soil reduces or eliminates the detrimental effects of aluminium

(Wright, 1937). Application of phosphorus lowers the solubility of

aluminium in the growth medium and results in relief from toxicity

(Wright, 1937). A phosphate-aluminium interaction was reported earlier

by Blair and Prince (1927) who found that Al toxicity can be overcome

by Heavy applications of soluble phosphates or by the application of

basic materials such as lime and basic slag. This is attributed in part

to the precipitation of aluminium phosphate in and on the roots (Nomoto

and Kisida, 1959; Vlamis, 1953; Wright, 1943). The application of acid-

forming materials increased the concentration of active aluminium in

the soil (Blair and Prince, 1927). Struthers and Sieling (1950) found

that the concentrations of Al, Mn, and Ca in the soil solution were

markedly increased when gypsum was added to the soil: a cation exchange

effect by the increased Ca and total salt concentration.

Iron toxicity

The concentration of ferrous iron in flooded soils is highly sensitive

to pH changes. The relationship between pH and concentration of dis-2+

solved Fe is as follows (Mai thi My Nhung and Ponnamperuma, 1966):

pFe2 + = 2 pH - 10.8 (Feo(0H)o present) 2+ 3 8

pFe = 2 pH - pH2S - 3.52 (FeS present)

2+ Mai thi My Nhung and Ponnamperuma (1966) reported that the Fe concen-

2+ tration reached 800 mg/1 after 5 weeks of submergence. Fe values of

800 to 1700 mg/1 leachate were found in flooded conditions, with or 2+

without incubation (Tanaka and Navasero, 1966). Fe concentrations of

5000 mg/1, 2 weeks after submergence, were reported by Ponnamperuma et

al. (1973), but values of 500-1000 mg/1 are more common, and some soils

apparently give very little. The peak values were observed after

30 days of submergence in acid sulphate soils in Kerala (Kaberathuman

and Patnaik, 1978). Iron toxicity in submerged acid sulphate soils is

the limiting factor for rice (IRRI, 1964, 1965). Concentrations of

ferrous iron above 500 mg/1 are indicated as toxic (Tanaka and Nava­

sero, 1966b; Mai thi My Nhung & Ponnamperuma, 1966). Tanaka et al. 2+

(1966) observed that rice leaves containing more than 300 mg/1 Fe

often exhibit iron toxicity symptoms. The physiological disorder of

rice known as bronzing in Ceylon and penyakit merah in Malaysia is

caused by excess iron (Lockard, 1956; Ponnamperuma et al., 1955).

There are many factors that aggravate or alleviate iron toxicity. A low

potassium content and the presence of sulfide induced iron toxicity

(Inada, 1965; Mulleriyawa, 1966; Tanaka and Navasero, 1966; Tanaka et

al., 1968). Iron toxicity can be alleviated by liming and by the addi­

tion of manganese dioxide (Ponnamperuma et al., 1965). Lime increases

2+

the pH and lowers the concentrations of dissolved Fe ; it also coun­

teracts physiologically the adverse effects of excess iron (Tanaka and

Navasero, 1966). In a pot experiment, Sahrawat (1979) studied the ef­

fects of two water regimes (continuous flooding and flooding with in­

termittent soil drying) on iron toxicity to rice in an acid sulphate

soil. He found that rice could be planted after keeping an acid sul­

phate soil flooded for a few weeks, when dissolved iron had dropped

below a toxic level; drying and reflooding on the other hand aggra­

vated soil acidity and kept iron in solution in concentrations toxic

to rice.

Low nutrient status

Although acid sulphate soils have sufficient total nitrogen, ammonifi-

cation under flooded conditions is inefficient.

The average quantity of nitrogen mineralized under aerobic, upland con­

ditions was 5.4% of the total soil nitrogen compared to 7.1% under

flooded conditions in acidic soil, at pH 4.5 to 5.5 (Borthakur and

Mazumder, 1968). In the soils of the Central Valley, Thailand, NH.-N

production during anaerobic incubation is about 3% per season (Kawa-

guchi and Kyuma, 1969). Addition of lime or phosphate increases N

mineralization (Hesse, 1961; Kawaguchi and Kyuma, 1969). Phosphorus

deficiency and strong acidity apparently retarded ammonification in

acid sulphate soils (Kawaguchi and Kyuma, 1969).

The phosphorus content of acid sulphate soils is low; phosphate is also

strongly fixed in these soils. Pham huu Anh et al. (1961) failed to de­

tect any available P with Olsen's method throughout the profile in an

acid sulphate soil in Vietnam. In Thailand, phosphorus deficiency in

acid sulphate soils was reported by Kanarengsa et al. (1972) and Matsu-

guchi et al. (1970). Tanaka and Navasero (1966a) found that acid sul­

phate soils from Vietnam and Malaya had little available phosphorus,

plants in pot culture having small amounts. Heavy dresssing of phos-

10

phate eliminated iron toxicity symptoms and resulted in normal growth

of the plants.

Moormann (1961) found that 800 kg rock phosphate per hectare failed to

give a residual response with rice in the second year in Vietnam. Hesse

(1961) and Watt (1969) reported considerable retention of phosphate by

fresh mangrove muds, and Watt also reported very low levels of phospho­

rus in the water of fishponds in acid sulphate soils in Malaysia. Iron

and aluminium played an important part in P fixation (Cole and Jackson,

1950; Kittrick and Jackson, 1955; Koshy and Bito-Mutanayagam, 1961;

Perkins and King, 1944). This agrees with the work of Tomlinson (1957)

who suggested that P was immobilized by iron. Black and Goring (1953)

indicated that inorganic P will be immobilized during the decomposition

of organic matter containing less than 0.2 per cent organic P. This

resulted in low available P in an acid sulphate soil. Potassium may be

deficient in some acid sulphate soils but, as in the case of calcium

and magnesium, no detailed investigations have been reported (Bloom-

field and Coulter, 1973).

Hydrogen sulphide

At the pH values of most flooded soils, most of the H„S in the soil

solution is present as bisulphide ion and undissociated HgS. Hydrogen

sulphide concentrations as low as 0.007 mg/1 have been reported to be

toxic to rice seedlings in culture solutions (Mitsui et al., 1951). A

number of nutritional disorders of rice have been associated with H„S

toxicity in different countries, depending on the timing and the symp­

toms of the damage (Baba et al., 1964; Tanaka and Yoshida, 1970).

Vangnai et al. (1974) gave some indirect evidence for sulphide toxicity

in rice on acid sulphate soil. Harmful concentration of H„S may be

present in acid sulphate soils and acid soils low in iron during the

first few weeks after flooding (Ayotade, 1977).

11

2.1.3 Reclamation and improvement

Reclamation measures for lowland rice include prolonged submergence,

leaching with seawater or rain water or a succession of these, addition

of lime or manganese dioxide or combinations of these.

Submergence

When a acid soil is flooded, the pH rises (Hesse, 1961; IRRI, 1963).

The increase in pH is mainly due to reduction of ferric oxides to dis-2+

solved Fe , a process that consumes acidity (van Breemen and Pons,

1978). If an acid sulphate soil is kept submerged until the pH in­

creases sufficiently, aluminium toxicity is eliminated and iron tox­

icity minimized (Ponnamperuma, 1964), and rice grows normally.

Farmers in Indonesia, Vietnam and Thailand have evolved systems for

cultivating rice on these soils. In Indonesia (Driessen and Ismangun,

1973), Bandjarese farmers of South Kalimantan manage the potential acid

sulphate soils by a very shallow tillage to deal with weed growth,

leaving the potentially acid sulphate material undisturbed; they use

old rice seedlings transplanted several times so that in the final

transplanting the seedlings are large enough to cope with toxic ele­

ments .

Moormann (1961) reports that the farmers in Vietnam grow rice over

quite a proportion of the Mekong delta, on soil with a pH of 2.8 when

aerated, by maintaining waterlogged conditions as much as possible.

In Thailand also, van der Kevie (1972) reports that a rice variety tol­

erant of deep flooding is the major crop on these soils.

The farmers' successful technique of submerging these soils is sup­

ported by pot and field experiments in other parts of the world. In

Guyana, Cate and Sukhai (1964) used pot experiments to demonstrate the

value of prolonged preflooding of toxic soils before planting rice.

12

Drainage and leaching

The development of acid conditions and the rise in soluble salts in an

acid sulphate soil after drainage is caused by pyrite oxidation follow­

ing air entry. It has been frequently proposed that acid sulphate soil

should be drained intensively to leach out these acids and soluble

salts. Leaching increases the pH, lowers specific conductance and low­

ers the concentration of aluminium and other salts, as well as the par­

tial pressure of CO. (Cate and Sukhai, 1964; Hesse, 1961; Ponnamperuma

et al., 1973). Many laboratory experiments have been reported on the

rate of oxidation of pyrite, and on the requirements for leaching of

acid sulphates. Richmond et al. (1975) showed that upon drainage, pH

decreased and SO.-S increased rapidly when the degree of pore water

saturation fell below 0.95. Fleming and Alexander (1961) conducted

leaching experiments in the United States and reduced the pyrite con­

tent of 2-3% to only 0.34-0.40% in 10 years time. In Malaysia Bloom-

field et al. (1968) managed to bring an original pyrite content of 2%

down to 0.36% (at 50 cm depth in 5 years time), using tile drains with

a 10-60 m spacing at 1 m depth. Experiments in the Medina experimental

polder in Senegal (Beye, 1973) where different drainage intensities

were imposed, showed the detrimental effects of intensive drainage.

Hart et al. (1963) estimated that one field season's drying would oxi­

dize about half the pyrite present. Another laboratory in Sierra Leone

(Annual Report, 1959) showed that daily leaching with seawater or fresh

water removed half the titrable acidity of the oxidized soils after

using five times the weight of soil, the rates of leaching being the

same for both fresh water and seawater. After leaching a soil of pH 2.6

with 15 times its weight of water, its lime requirement (to pH 5.2) was

lowered from 38 to 8 tons CaCCL per hectare per 15 cm. Kivinen (1950)

reported an increase in pH from 2.5 to 3.7 when small samples of acid

clays were leached with copious quantities of water. It should be kept

in mind, however, that the conditions for oxidizing and leaching small,

well homogenized samples in the laboratory are very different from

those in the field.

A number of one-season trials have been reported. In Sierra Leone,

where the excess of rainfall over evaporation in the rainy season may

13

exceed 1200 mm leaching by rain is an extremely slow process and may

take 10 years to complete (Annual Report, 1959).

Experiments on leaching with seawater or brackish water have been re­

ported from Sierra Leone (Hart et al., 1963) and Guyana (Evans and

Cate, 1962). Bower and Hardier (1970) found that leaching an acid sul­

phate soil with seawater removed a large amount of Al, increased pH and

exchangeable Na and K, and slightly depressed exchangeable Ca and Mg.

It has been suggested that the saline water acts in the same way as a

neutral salt solution in the laboratory experiments so that exchange­

able aluminium is displaced from the soil by the basic cations in the

seawater.

Liming

Acidity can obviously be corrected by liming (Chang and Puh, 1951,

McLean et al., 1964; Ponnamperuma, 1960). Lime supplies Ca, removes

toxic aluminium by hydrolysis and precipitation and increases the

availability of phosphorus (Black, 1968, Coleman et al., 1958, Khallik,

1959, Mehlich, 1946; Ponnamperuma et al., 1973, Pierre, 1938, Struthers

and Sieling, 1950, Tisdale and Nelson, 1966). Liming decreases soil

acidity and counteracts the poor physical conditions brought about by

leaching (Hesse, 1961). Lime added to rice soils under flooded condi­

tions increased mineralization of soil nitrogen and released about

100 per cent more NH,-N from the soil during the first 14 days of

waterlogging (Abichandani and Patrick, 1955, 1961). Aslander (1952)

found that addition of lime resulted in rapid decomposition of organic

matter. Nambiar (1961) attributed this to the stimulation of microbial

activity. Another important effect of liming is to increase the avail-2+ ability of most plant nutrients (Truog, 1948). Lime decreases the Fe

in the soil solution, hence iron toxicity can be alleviated by liming

(Ponnamperuma, 1958, 1960; Subramoney and Balakrishmakurup, 1961,

Takigma and Kanaganayagan, 1970, Tanaka and Navasero, 1966b). Leaching

and liming together has improved pyritic muds (Zuur, 1952, Attanada,

1971). Previous leaching lowers the lime requirement substantially by

the removal of acidic substances.

Lime rates of 3 to 6 tons CaCC^/ha are generally best and several field

14

and pot experiments indicate that higher applications are even harmful

(Pham Huu Anh et al., 1961, Ha, 1970; Park et al., 1971; Yang, 1976;

Sombatpanit, 1975; Takahashi et al., 1979). The reasons for the over-

liming effect are not clear, but it has been attributed to temporary

alkali damage (Park et al., 1972) and formation of sparingly soluble

calcium phosphate compounds (Sombatpanit and Wangpaiboon, 1973). Ap­

plication of large amounts of the slower acting wollastonite (calcium

silicate) had no overliming effect (Park et al., 1972).

A three-year experiment in Rangsit, Thailand (Suthdhani and Glasewig-

gram, not dated) to study the effect of liming on the yield of rice, at

three rates of 1875, 3750, and 7500 kg slaked lime per hectare recorded

a yield increase from the first year with a tendency of cumulative

benefit.

Other treatments

Manganese dioxide retards soil reduction by virtue of the high standard 2+

oxidation-reduction potential of the MnCL - Mn system. Manganese

dioxide improved the growth and yield of rice in an acid sulphate soil 2+ 3+

because it depressed the concentration of water-soluble Fe and Al

(Mai thi My Nhung and Ponnamperuma, 1966; Ponnamperuma et al., 1965,

1973). A reclamation study of a kosh soil in Bangladesh (Islam and

Shah, 1968) showed that liming and MnO„ gave the best growth. This re­

sult was attributed to (a) the depression of aluminum toxicity and (b)

the rise in pH and the accompanying increase in the availability of

nutrients.

2.1.4 The need for research to monitor chemical changes and plant

performance under various reclamation measures

Many laboratory experiments have determined the rate of oxidation, e.g.

acidification and leaching, but very little work has been done in field

conditions or on undisturbed cores, which would be the nearest approxi­

mation to the field situation. The rates at which the resulting sul­

phates are leached and the degree of acidity that develops on oxidation

15

and leaching are obviously of great importance in the improvement of

these soils for agriculture.

Field trials and pot experiments indicated that acid sulphate soils can

be put into production for lowland rice by leaching, liming, liming

plus leaching, application of manganese dioxide or prolonged sub­

mergence. Over a large area the use of lime or manganese dioxide is not

economically feasible and prolonged submergence may not be possible be­

cause of inadequate possibilities for water control. Therefore, a study

on the effects of different agronomic and water management methods on

these soils is of primary importance. Different packages should be

based on hydrological factors, availability of irrigation water, crop­

ping intensity, cropping schedule and present management practices. The

physical and chemical changes induced by different management practices

should be well monitored.

Objectives:

The objectives of this study are:

1. To study the dynamics of chemical changes in soils with time under

different water management and agronomic packages.

2. To find a practical method or methods of reclamation and improvement

of acid sulphate soils on the basis of the results under objec­

tive 1.

2.2 Materials and methods

2.2.1 Preparation of undisturbed soil cores

Research on acid sulphate soils has largely been of two main types:

fundamental laboratory experiments on individual, disturbed soil sam­

ples and reclamation trials in the field. The results from the former

are not directly transferable to field conditions; the latter generally

do not allow for sufficient measurements to determine the rate and ex­

tent to which the different processes influence soil conditions and

crop growth.

Undisturbed soil cores of large size are desirable for the study of the

16

dynamics of soil physical and chemical changes in a closely controlled

system that is similar to the field situation. Techniques to obtain un­

disturbed soil cores have been reported by different workers (Bannink

et al., 1977, Black and Raines, 1978, Craswell and Castillo, 1979,

Mielke, 1973 and Watson and Lees, 1975). These methods are used to col­

lect either small samples or large samples mostly for physical studies,

but are not suited for the study of water and solute movement without

contamination in a system with several growing plants. For this purpose

a lysimeter drum was developed that met the dimensional requirements of

the specific studies and could still be handled in the field situation

(Le ngoc Sen, 1982a).

Design requirements and construction of the lysimeter drum

The design specifications for a lysimeter containing an undisturbed soil

profile should satisfy the following requirements:

a) The lysimeter drum should be of a size and weight that allows collec­

tion of a representative soil profile core in swampy areas.

b) Samples should be large enough to accommodate several rice hills

until maturity to minimize boundary effects and to average out the

effects of macrostructural heterogeneities in the rhizosphere on the

growth of the rice.

c) The gross weight of the soil profile core should be small enough to

allow transport to the experiment station.

d) The materials used should be resistant to corrosion and should not

contaminate the soil profile core.

Available oil drums were used to construct the lysimeters. Each has an

inside diameter of 60 cm and a length of 90 cm (Fig. 2.1). Both ends of

the drum were cut out by hammer and cold chisel. The rolled edges of

the drum were retained. The reinforcement ribs around the drum wall

were filled with two-component plastic putty to straighten the inside

wall. Holes were drilled in the drum in different positions along its

length for later insertion of perforated PVC drainage pipes, soil

moisture sampling filters and tensiometers (Fig. 2.1). These are used

to drain the water from the profiles, to monitor solute concentrations

and to measure changes in soil moisture tension with time along the

soil profile. The holes were sealed temporarily by epoxy-painted pieces

17

Holes for later intersection soil-water sompler Perforated PVC pipes

Fig. 2.1 Diagram of a lysimeter.

of sheet metal glued on with two-component epoxy glue. Galvanized iron

covers were fabricated for bolting to the bottoms of the drums after

collecting the profile cores (Fig. 2.1). The drums and covers were

painted with epoxy paint to prevent rust and contamination of the soil.

Collection of soil profile cores

The procedure used in obtaining the samples was to press the drum into

the soil in depth increments of 5 to 10 cm by means of a wooden bar

placed on top and six to ten persons stepping on it (Fig. 2.2A).

Before each incremental insertion of the drum the soil was trimmed from

around the drum to a depth of 5 to 10 cm below the bottom of the cut­

ting edge, so that only a small amount of soil had to be pared away by

the cutting edge when the drum was pressed into the soil. The process

was continued to the desired depth. The soil below the cutting edge was

then cut in a cone shape to prevent fracture of the core while it was

dragged out of the profile pit (Fig. 2.2B). One side of the profile pit

was cut to a 45° slope. The filled drum was tied with rope, turned 45

degrees (Fig. 2.2C), laid on a wooden pallet and dragged up to the

ground surface along the sloping side of the pit. The excess soil ma­

terial at the bottom was trimmed level with the cutting edge. A galva­

nized iron cover was then bolted on to close the bottom of the drum

(Fig. 2.2D).

If more than one core was to be collected the drums were placed in a

row and inserted and excavated in sequence to save digging effort.

Experience has shown that ten men can complete collection of 5 cores

per day.

18

Fig. 2.2 Scheme of field operating procedure to take undisturbed soil

cores.

Installation and instrumentation of lysimeters

The joint between bottom cover and drum was sealed with two-component

plastic putty. A perforated PVC drainage pipe of 2 cm outside diameter

wrapped with nylon mesh (mosquito screen) was installed from the side

of the drum at a depth depending on the treatment.

Soil moisture sampling filters, consisting of a Whatman filter tube

wrapped with micropore material, were connected with glass tubes and

supported by a plastic pipe with the same outside diameter as the

available filters (Fig. 2.3). These filter assemblies were installed

horizontally at different depths along the profile.

-Rubber Stopper

-Plastic Tube

-Gloss Tube

Rubber Stopper

Glue Joint

Gloss Wool

•Whatman Filter Tube

•Cuorr: Sand

Plastic cover

Fig. 2.3 Soil-water sampler components.

19

Fig. 2.4 Lysimeter cylinders wrapped with fiberglass blai

First rice crop near maturity.

Fig. 2.5 Lysimeter cylinder with vacuum pump and collecting tubes

attached to the soil moisture sampling filters.

20

Before installing the filter assemblies, a narrow hole was bored out

with a soil auger made of plastic to prevent contamination. After in­

stalling the assemblies, the joints of the plastic pipes with the lysi-

meter drum were sealed with two-component epoxy glue. The tensiometers

were installed in the same way from the opposite site of the drums. A

fiberglass blanket was wrapped around the lysimeter drums to minimize

horizontal heat transfer resulting from direct sunlight on one side of

the drums (Fig. 2.4). A vacuum pump was used to draw soil solution from

the sampling filters into collecting tubes (Fig. 2.5).

Cost and performance

The cost of this lysimeter is about US $ 60: one third of the cost of

fiberglass or PVC pipes of the same size. Forty-eight undisturbed soil

profile cores, 80 to 85 cm long, were obtained from different places in

the Philippines. Eight cores were used for the primary test and the

other forty were used to set up the experiment. Water movement slowed

down somewhat after leaching the cores for one month, probably due to

closing of the initial gap between the clay soil and the moisture

sampling filters and drainage pipes. In all other respects, the per­

formance of the lysimeters was stable over the two-year period of ob­

servations , covering three cropping seasons.

2.2.2 Experimental treatments

Two acid sulphate soils from Aparri and Sinacaban, Philippines were

used for this study. Information about their profiles is given in

Appendix 2.1 and some of the physical and chemical properties are pre­

sented in Tables 2.1 and 2.2.

The combination of agronomic and water management packages applied to

the cores is shown in Table 2.3. The lysimeters were arranged in four

parallel rows 1 m apart, with 10 lysimeters (0.5 m apart) in each row

and the treatments were randomly distributed. Each treatment was re­

plicated two times. IR36 rice variety has been used. In treatments 3,

4, 5, 7, 8, 9 and 11 lime was mixed with the upper 20 cm of the soil

20 days before transplanting. N, P, K fertilizers were applied at the

21

a CU /~\ <a a rH a, o o.

OH w CG ^ ^ +J a o o.

i a 0) S *

01 1-1 X I n) 4-1 U CO u 4-> X

H

H ÛC

O o r H

^ a cu a ^̂

o H O

00

s

M

a

00 o o !-H • — . & eu B

i*

i H tO U

• r l

S CU

43 U

O H

U • r l

rl fl M M O

eu 4J •H

>» O i

ca cu

• r l •U b 1) & O u Cu

^̂ ** v—/

e—s

» s _ /

( j H

M a

« o.

43 •P P. CU

• O

i-I •rl O

UI

s u — ai S •o CU

4-> a u CU a

J3 M eg h

>rl

S O

4-1 U IS 1-1 4J X CU

1 - 1

1 - t

rH ~ * 0\ CM

oo o m m co m o en C M C M C M CM

-* •* o -ï a> ai o CM

i-i CM

»o ai r— co CO CM rH CO

O h - rH Crt

r^ co r- CTI 1-1

\0 O rH UI

CO CO *sf cj^ rH rH r-l rH

CO CO *st" CO

r H CM » t CM CO CO

u u CO

**

o

o

o

**

rH m o

o 0>

-*

o

o CM

CO

CM CO

O

co MS

rH 00 O O O rH

f< - * - * 00

a\ f t

CM

<t

O

m

o co ~~. m CM

1

O

VO CM

o\

CO

CM

— O

•tf 1

o co •••s,

m CM

a\ CM

r^

co

co

~*

o M3

1

VO

>* "̂ , O

-*

CM f*

m

co

CM

MD

O C*

1

O M3

co CM

CO 0 0 0 0 O ft r-t VO - * CO

\0 r-t CM CM

o co 0\ CM rH CM

CO

m

oo

M5

CM

00

CM

CM

CM

CM

m

r-i

m

co

r^

VO

f t

o

~* m

m

M3

m i-i

CM

O

o

o

m

co

oo

en

co I-H

f t

o

f t

<f

m

CM

f t

f t

oo ft

f t

o

co

co r* CM CO

a ID

X I

a u id d

•H c/>

a\

«* r H

r H CO

co o CM

CO CO

00

m CM

CM CO

«tf r* CM

OS CO

** CTi CM

oo co

i n en »-H I-H

v£ CO

f t

*3

f t

VO

m r H

>̂ , O rH

1

O

CM

**

00

co

•*

m C M

O CM

1

m ft

o f t

«* ~*

m

CO

-» «3

O

»* 1

m C M • — .

o CM

O m

co

CO

o

M3

O r-

i

o >*

CM m

o\

CM

o

MS

o o r H

1

O r—

22

same levels for all treatments. The experiment was carried out ac­

cording to the following scheme:

- 10 July 1980 - 30 August 1980 : the first leaching period

5 September 1980 - 16 November 1980 : the first rice crop

- 16 November 1980 - 30 May 1981 : the soils were kept submerged

with water to wait for soil

moisture equipment

- 17 June 1981 - 30 August 1981 : the soils of the respective

treatments were drained to

subject them to the oxidation

process.

1 September 1981 - 30 September 1981: the second leaching period

6 October 1982 - 15 December 1981 : the second rice crop

- 15 January 1982 - 1 April 1982 : the third crop

An unexpected typhoon occurred in November 1981 affecting partly the

rice yield of the second crop.

Table 2.2 Particle size distribution of different depths along soil

profiles of Aparri and Sinacaban acid sulphate soils.

textural Aparri analysis

soil depth (cm) clay (%) silt (%) sand (%)

11.1

29.7

47.7

18.8

21.1

25.4

41.4

49.4

50.0

0 - 25/30

25/30 - 40/46

40/46 - 60

60 - 90

0 - 10/15

10/15 - 20/25

20/25 - 40

40 - 70

70 - 100

53.2

32.2

15.2

10.2

20.0

9.0

8.7

15.0

14.0

35.7

38.1

37.1

71.0

Sinacaban

58.9

65.6

49.9

35.6

36.0

23

Table 2.3 Treatment combinations used in the drum experiment.

Treatment Water management

Deep Shallow

Drainage Drainage Flushing Percolation Mulching Liming 1)

replicates

1

2

3

4

5

6

7

8

9

10

11

0 1

x

1) Deep drainage:

Shallow drainage:

Flushing:

Percolation:

Mulching:

Liming, 0: 1:

2:

drain at 80 cm below surface only applied during leaching periods drain at 40 cm below surface only applied during leaching periods renewal of water standing on the surface every 3 days during leaching periods removal of excess water through the drains during the growing season application of 5 cm of rice straw during dry season no lime 1 ton/ha for Aparri soil and 1.25 tons/ha for Sinacaban soil 2 tons/ha for Aparri soil and 2.5 tons/ha for Sinacaban soil.

Lime was applied 1 week before transplanting rice. During the growing

periods, water was maintained 15 Cm depth above the soil surface and

the drains were blocked.

24

2.2.3 Analytical methods

The physical and chemical characteristics of the soils were determined

according to the following scheme:

1. Textural analysis: pipette method

2. pH: pH meter

3. EC: EC meter with 1:1 extract

4. Sulphate: gravimetric method

5. Soluble and exchangeable aluminium: atomic absorption spectro­

photometer

6. Free oxide iron: atomic absorption spectrophotometer 2+

7. Mn : atomic absorption spectrophotometer

8. Total phosphorus: Olsen method (Black et al., 1965)

9. Total carbon: Walkey and Black Method (Black et al., 1965)

10. Buffer lime requirement

11. Extractable cations: extraction with ammonium acetate and CEC

(Black et al., 1965)

12. Total nitrogen: Kjeldahl method (Black et al., 1965)

13. Pyritic sulphur: (Begheijn et al., 1978)

Surface water, drainage water and the soil solutions along the soil

profile were collected weekly for the first cropping season and bi­

weekly for the second and third cropping seasons. The pH, EC of surface

water and soil solutions were measured directly by pH meter and EC

meter, respectively. The soil solutions were acidified with a few drops 2+ 2+

of 6NHC1 to prevent oxidation of Fe and Mn . Subsequent analysis of

the acidified solutions were made. AI, Fe, Ca, Mg, K and Na were de­

termined directly by atomic absorption spectrophotometer.

Observations on the symptoms of deficiencies and toxicities were made

on the rice plant during the growing season. Measurements were carried

out at weekly intervals on rice plants including plant height, number

of tillers, number of panicles, percentage of tillering, percentage of

flowering.

After the harvest, grain/panicles and straw weights were determined.

The straw was analyzed for N, P, K, Mn, Fe, AI, Ca, Mg.

25

2.3 Results and discussion

Before starting the experiments, the filters and drainage pipes were

installed along the soil profile to collect soil water solutions for

monitoring the chemical changes during leaching periods and rice grow­

ing seasons. Although the soils were carefully maintained saturated

with water before setting up the experiment, some of the lysimeter

drums were leaky and pyrite oxidation was taking place. Results there­

fore yielded some variations among treatments. In the following sec­

tions the physical and chemical properties of each soil will be pre­

sented and discussed.

2.3.1 The amount of drainage water collected under different

water management practices during the first and second

leaching periods

Table 2.4 shows the amount of drainage water collected under different

water management practices in Aparri and Sinacaban acid sulphate soils

during the first and second leaching periods. Both soils have highest

amounts of drainage water when deep drainage was imposed. In Sinacaban

soil, the amount of drainage water collected during the second leaching

period was higher than the first one. In this soil large amounts of

Table 2.4 The amount of drainage water collected under different water

management during the first and second leaching periods.

Water management treatment

Flushing

Shallow drainage

Deep drainage

The amount of drainage water

Aparri

First leaching

100

140

210

Second leaching

30

60

110

(mm)

Sinacaban

First leaching

140

200

300

Second leaching

100

340 (250)

450

Value in parenthesis is the amount of drainage water in shallow drain­age with mulch treatment.

26

Table 2.5 Average soil moisture content (by weight) and n-value of different depths

along the profile of Aparri and Sinacaban acid sulphate soils at the end of

dry season, 1981.

Soil

depth (cm)

Treatment

1 2 3 4 5 6 7 8 9

10 11

1 2 3 4 5 6 7 8 9

10 11

1 2 3 4 5 6 7 8 9

10 11

1 2 3 4 5 6 7 8 9

10 11

0-10

12.0 15.3 10.4 24.4 15.6 14.6 12.7

53.2

19.9

33.9 34.5 19.0 43.1 45.2 36.3 21.7

-87.9

-15.2

0.05 0.10 0.03 0.22 0.10 0.09 0.06

0.60

0.16

0.51 0.52 0.11 0.75 0.81 0.57 0.18

1.93

0.05

10-20

40.7 44.0 27.8 39.4 38.9 34.6 34.0

62.0

36.0

72.1 59.9 80.4 71.1 81.5 82.5 82.2

-94.7

-65.6

0.43 0.48 0.26 0.41 0.41 0.35 0.34

0.72

0.37

1.68 1.31 1.93 1.65 1.96 2.00 1.99

2.36

1.48

20-30

41.4 61.4 50.9 43.2 51.3 52.4 53.5

65.0

47.1

91.3 68.0 92.2 87.1

118.2 101.9 101.5

-99.2

-71.9

0.44 0.70 0.56 0.46 0.57 0.59 0.60

0.75

0.52

2.06 1.42 2.08 1.95 2.80 2.35 2.34

2.28

1.53

Soil moisture, g

Aparri

30-40

64.7 60.3 79.5 52.6 68.8 63.9 71.6

93.7

49.7

Sina

106.9 86.7

113.2 134.1 141.2 99.1

123.7

-131.0

-86.9

n-va Apa

0.82 0.75 1.05 0.64 0.89 0.81 0.93

1.27

0.59

Sina

2.49 1.94 2.66 3.24 3.43 2.28 2.96

3.16

1.94

40-50

91.4 78.5 79.9 75.2 70.3 85.3 79.3

108.9

61.9

caban

111.2 113.8 142.3 197.1 159.3 107.9 100.8

-144.2

-70.8

lue rri

1.23 1.04 1.06 0.99 0.91 1.14 1.05

1.50

0.78

caban

1.93 1.98 2.55 3.64 2.88 1.86 1.72

2.58

1.12

per 100

50-60

96.9 73.4

101.0 85.7

102.6 104.5 88.8

-

75.3

120.1 133.6 137.2 157.4 159.2 149.2 136.0

-160.0

-90.1

1.59 1.14 1.67 1.37 1.70 1.74 1.43

-

1.17

2.10 2.37 2.44 2.85 2.88 2.68 2.42

2.90

1.50

g dry matter

60-70

117.2 105.9 102.9 103.7 102.0 123.9 118.3

97.7

109.1

188.6 170.0 178.2 142.3 175.2 122.7 163.0

-195.2

-144.1

2.00 1.78 1.72 1.73 1.70 2.13 2.02

1.62

1.84

3.47 3.10 3.27 2.55 3.20 2.16 2.96

3.60

2.58

70-80

-107.3 103.2

-109.9

--

-

121.6

192.6

-159.0 175.8

-101.6

-----

-1.80 1.72

-1.86

--

-

2.08

3.49

-2.83 3.16

-1.70

-

-

-

27

acidity developed during the oxidation process, which required a large

amount of water to leach out the acidity and toxic elements.

During the cropping season, the amount of percolation water were 60 and

140 mm for Aparri and Sinacaban, respectively.

2.3.2 Average soil moisture content (g per 100 g dry matter) and

n-value of different depths of Aparri and Sinacaban soils at

the end of dry season, 1981

Irrespective to soils and water management practices, the soil moisture

content increases with depth (Table 2.5). There were large differences

in soil moisture content between treatments. In both soils, the highest

soil moisture contents were observed in shallow drainage with mulch

treatments.

The n-values of different layers in the soil profiles were calculated

using formulae developed by Pons and Zonneveld (1965). In Aparri soil

n-values at 10-20 cm depth in both the shallow (without mulch) and deep

drainage treatments were less than 0.4 (Table 2.5). The shallow drain­

age treatments with mulch reduced the water loss by evaporation, resul­

ting in higher n-value. Higher n-values were observed in the lower lay­

ers of different treatments. In Sinacaban soil, n-values were about two

times higher than those of Aparri soils. At the 10-20 cm depths, n-

values were about 0.70, whereas n-values greater than 2.0 were found in

the lower layers. Similar to Aparri soil, the shallow drainage treat­

ments with mulch produced higher n-values.

2.3.3 Chemical properties of the soil solution of Aparri and

Sinacaban acid sulphate soils during the first leaching

period and the first crop

2.3.3.1 Aparri soil

In this soil, the initial pH-values were nearly all above 4.0. During

the leaching period, the pH value of all treatments increased by about

0.3 unit, except in treatments 10 and 11 (Table 2.6). When the soil was

28

W u

•H >H

m x l 4-1

a •i-i

r-H •H O 10

•H U U <0 P. < 4-4 O

0) u ia

>« ki 3 u

iH •H O 1»

» O .-1 ai

x i E u

o CM

4-1

a

•H 4J 3 O

1-1 •H O 01

m x l 4J

4-1 O

II) ai

M

> U M

•o a

« s a<

VO

CM

Cl iH X I

« H

a< O

u

ai u

•H kl

•M

kl •H 4-1

ai XI 4-1

M d

•H kl 3

T3

d

« •o o

•H kl ai a. 60 d •H

XI U

ai rH

a o ki u 4-1 »1 kl

•H h

P.

•a o

•H kl ai a M d

•H Xi U m ai

r-l

4-1 m u

•H

fe

4-1 Vi 01

fc a)

XI ai ki o

4-1 m X I

01 m »

CM

OC d

•H 4-> d a

1-4

& M d <o ki 4-1

kl ai 4J 4-1

<

T3 d

W

4J kl a 4-1 en

4-1

d ai

S a ai ki

H

ai 00

« ki ai

> <

CM

ai «

i-i p. ai «

ai 60 a ki ai > <

CM P< ai

os

l-H a< ai «

ai 00

ki ai

> <: CM

a< V

os

r-t a< ai

OS

ai 00

ki ai > <

CM P< ai

os

r-i p* ai

os

\ O r * C M r ^ r ^ \ o o o v £ » o o < t o o

i o i O L O i n i o i / i t / i i o m ^ i / 1

r > - i n o o o o o o c M O v o •» m ^ >o Ml m K l l O • * I

^ ( O l f l - Ï C A - J i n H O ^ O O

v û ^ ^ t i o i / i i o ^ o i o N ' ^ i n

c o c o o o i n o o t ^ i - i o o c o c o v o m m - J m •» J m • * m - J m

\ o o o o a \ r ~ - o o N i n

O * 0 \ Û H N N N N C J P I \ û v û ^ ^ u - i ^ ^ i / i ^ ï v o - d - c o

H ' j o i i O N O M n o M « ! »

> * ( O v O M i n i n M N O \

- j - ï ( O i o c i r - n o m i

i ^ - c r i i - i » - i c^^ , r^r - -^ , oooo H i / n o i / i M o n c A n m - t

M o o o o m H o n o i i n ^ o

O P ~ I - ~ O M 3 0 0 V O C M C M

m t o n v o n o o n c A f l O i

C O O O O C A V Û f f l O N t N I ^ O

« u n o - j - M H n o o M n ifl

i/i S

C O C O O O u l v O v O O O O C O C O v O

t l O O O O W C O I ^ M

O M 3 \ O i - i c o r ^ c s i r ^ i o c o \ o

H O > * N - J H l ^ ' J N O > 0 i r ) i r ) « * i n ~ t - * » d - - * m < r c o

OCMCO<T\CMi - lOCOU">OM3

W M 5 ~ * * O C O O N V O » * C T \ C M r - . a \

c i - f ' ï i / i N O f l i M n i n - »

- j o o o - f M M n c o N

u i c o c o v o c o o o c o o c o i

o o o o i n c M i - i - * c i o \ C M r ^ o > H i n m > t N N m « ! M n - t

i - l v O r - m O v O C O C M U I i - l r H

o o O M 5 r - o * * o > c M O v O v O

v o c M o o c M v o « * w m o

n n - t o o o M O N n o i

4 n i - H a \ r * . * 4 " C T i r ^ o o c M » - i ^ Q O O O V O O N « O H H t O \ Q

i - i c M c o ~ * i n v o r » - o o a i O r - i H N ( o - j i n , O M O o i o n

29

xl 4-1

a •H i - l • H O to

c co « a u a d

• H

</> <M O

eu u co

m k i

d CO

1-1 • H O

co

» O i H

eu X I

a u

o CN

+J

co

d o

• H 4-1

d 1-1

o u

1-1 • r i O «1

01 xl • P

M-l O

CI 1

1-1 M

> U W

d a

« p <

tu x l H r~

CM

eu i - i X I m

H

O i 0 Vi U

CU

U

• H h

• 0 CO h

• H m

eu XI 4-1

CIO d

•i-t ki d

•o

•o d «t

t ) o

• H h 11

a. 0 0

d • H X I U al CU

• M

CI)

k l • H <rl

a o k i

u 4-1 U k l

• H ( X

w a

•v o • H

k l

CU

P i

M d

• H X I U CD <J

r - (

* J CO k l

• H f"H

4-> CQ

0)

t co X I

eu ki o

M-l

eu X I

en M eu eu S

CM

CK

d • H •M d 10

i-i d CO d 10 u 4-1

k l

eu • u

m <

•o d

(d

4-> k l C0 4-1 V)

4-1 d eu

a * J

co eu k i

H

eu 00 10 ki eu > <

CN P . eu «

i - i Ci. eu

«

eu 0 0 C0 k l

eu

S CM

CU

« 1-1

P i

eu «

eu eo co k i

eu > <

CM O i eu «

i - i

o. eu «

eu ao co k i

eu > <

«M P< eu as

1-H

<U

«

c n o o r H o o v o « 3 ~ » M 3 i n c i c n

V O I O ^ V O ^ ^ V O L O ^ O ^ I O

n ^ o s c o ^ o o o o CM

v o m v o v o t c - M D m m v û • vo

4 0 N 0 - * * O - » O n c M

v O ^ V O N \ O v O ^ C ^ 3 r ^ < d ' V O

O m c M v O O \ O U " > O C M C O « t f

m - l > * ' c r - ï i n - * ' * i n - * - J

« N O l C M O C O M n o O

m - * c o ~ » ~ * m ~ * c o > a - i

0 0 0 » * O O O I " ~ O M 5 \ O C O - t f

t s n m N H O i n ^ o - c o o c M

r ^ ^ - C M C n c M 0 0 L O ^ 3 ' < , r - l v û rH CM

o i n c M m c M c n « a - o r ^

r ^ ^ c M c M C M o o r ^ r ^ i o I

n r i i n e n o n T i M O f l O c s

r ^ - a - o c o c M r ^ c o c M O i - i v o rH CM

« C T C O H C A S O L n ^ C O r H ^ O O

r ^ - c f r t f O N M / i ^ ' f o i n rH CM

M O O O l s c n O C O O M

N i n c N c n c o p ^ r ^ c o i n i

>o »o >» H eo co H m o - f co

r ^ ^ t c o ^ r - i r ^ c o i - i c n o i o i-l CM

c O H e o > 0 ' * o i n i ~ - H CM ^

v O M c o c M o o c n M n r *

i n - c r o - ï e o m ^ o i » * i

o o r ^ o o r — c o e n v o c M « *

m - * i » i i o i n > * - J ' n i n ' * > t

0 > * C O v O M S v O O O r ~ - C O O C M

^ c o c o c o c o ^ c o c o ^ ^ c )

c M t ^ i o - a - i n c M e O L O ' - i

• j n c i c o n m c o n - ï i

C O H H C O O O O N C n v O O N

c o c o c o c n c o ^ c o c o ^ ^ c o

W M D C M C T l ~ * a i i - i r - O O O i - I C O

o o i n c M c o i - i r ~ ~ t « * ~ * o m rH CM

e o r ^ c o v o m ' - i c M ' J ' O

f - - ~ » c M c o c M r ^ r - . o o u - > i

« * r ~ ~ Ï C M C M O C M C M O i - i c O

O M f l l » l C O r t M ^ H I > 1 0 i n i-l CN

m r i c n c o o x j o n - J N u i

N * Û C M 0 0 I O C O r ^ \ O O | H \ û C M i - I C M r - l i - I C M i - I C M C M C O C N

N ! » ) • * H f l N 00 CM VO

O ^ H C I N O O N O l C O i - I C M C M C M C O C M C O C M

0 O « * C M > * O 0 - * C N ~ * C M C M i r )

• t » c n ^ * i > . > o o i o i n H > o N rt CM H N H CN H C O M

r i c M c o « j r L n v o r ~ o o c ^ O i - i > - i c N e n - » m M S t - - o o c n o i - i i-H i-l rH rH

30

flooded with water during the crop growing period, pH values of all

treatments increased by about 0.8 unit (Table 2.6). Imposing water man­

agement practices to the soil, a considerable amount of salt was leach­

ed out or flushed away, resulting in a electrical conductivity drop of

all treatments to about 4.5 except with treatments 6 and 9 (Table 2.6).

There was only a slight change in EC value during the first crop. 2+

The Fe concentration in the solution at 20 cm depth below th

surface remained below 100 ppm during the cropping season.

2.3.3.2 Sinacaban soil

The Sinacaban soil was more acid, with initial pH values below 4.0 and

often below 3.5. Similar to Aparri soil, pH values of all treatments

increased when water management was imposed and during the crop growing

season (Table 2.7). In both shallow and deep drainage treatments, EC

values decreased substantially values whereas in the flushing treat­

ments (8 and 10) EC values remained high during this period

(Table 2.7). There was little change in EC values of different treat-2+

ments during the growing period. The Fe concentration at 20 cm depth

was 700, 1000 and 2000 ppm for one replicate of treatments 6, 7 and 8 2+

respectively. About 300 ppm of Fe were observed at 20 cm depth in the

other treatments.

2.3.4 Chemical properties of the soil solutions of Aparri and

Sinacaban acid sulphate soils during the second leaching

period, second and third rice crops

2.3.4.1 Aparri soil

Table 2.8 shows the average pH values over the profile during the

second and third crops. There was no marked difference in pH among

treatments. The movement of oxygen to the lower layers, needed for

pyrite oxidation, was hindered by the high percentage of clay in the

surface soil (Table 2.2) and the absence of cracks. Even imposing deep

drainage to this soil, pH values in all layers remained higher than 4.0

31

Table 2.8 Average pH values of Aparri soil in the profile and during

the second and third crops.

Treatment Rep. J2ÎL Rep, Average

1

2

3

4

5

6

7

8

9

10

11

5.9

5.3

6.1

6.4

6.3

5.4

5.7

6.0

5.8

6.1

6.0

5.8

6.0

5.7

5.5

6.0

5.7

5.6

5.8

5.9

6.0

5.9

5.7

5.9

6.0

6.2

5.6

5.7

5.9

5.9

6.1

6.0

Table 2.9 Average pH values during the second and third crops at dif­

ferent soil depths in Aparri soil.

Treatment

1

2

3

4

5

6

7

8

9

10

11

soil

depths (cm)

0

6.8

6.8

7.6

7.5

7.2

6.8

7.5

7.9

7.7

7.4

7.2

20

6.2

5.4

6.4

6.1

6.7

5.7

6.0

6.6

6.2

6.6

6.6

pH

40

6.5

5.2

4.7

4.5

5.3

5.9

6.5

5.0

4.5

4.5

5.8

60

5.1

5.0

4.4

5.3

5.3

4.2

4.4

4.3

6.4

6.4

4.9

80

5.5

5.6

5.7

5.7

5.9

5.9

4.3

4.2

5.0

5.0

4.5

32

(Table 2.9). The Aparri soil, therefore, will not cause severe problems

upon reclamation.

2.3.4.2 Sinacaban soil

* Effects of lime on the chemical properties of deep drainage treat­

ments .

The changes of pH values in the soil solution of surface soil (20 cm

below the surface) during the second leaching period, the second and

third crops are shown in Fig. 2.6. Even in the treatments with lime,

the initial pH values were again well below 4.0. Regardless of lime

levels, pH values increased as drainage proceeded. The overall trends

in the changes of the pH values of the soil solution appear to be sim­

ilar (Fig. 2.6). There was little influence of lime on the pH of the

soil solution during the second crop, because the acidity remained high

during this period. The influence of liming, however, is illustrated by

the frequency of occurrence of pH values below 3.5 in the surface water

and in the soil solution at a depth of 20 cm during the second crop

(Fig. 2.7). The frequency of pH below 3.5 in the surface water was 100

and 50 percent at application of 1.25 and 2.5 tons lime per ha, re­

spectively whereas a lower percentage was observed at 20 cm depth.

During the third crop, and at both lime levels, the pH values of the

soil solution at 20 cm depth increase to nearly 6 (Fig. 2.6). The lower

pH values after application of 2.5 tons lime/ha could be explained by

the upward diffusion of acidity from greater depth.

-EC

The electrical conductivity in the 20 cm depth of 1.25 tons of lime/ha

became lowest during the leaching period (Fig. 2.8). Under the flooded

conditions during the second crop the electrical conductivity in­

creases , regardless of lime levels. The differences in EC values di­

rectly after leaching remained during the second and the third rice

crops. The high EC values of the treatments with 2.5 tons of lime/ha

33

pH

6 I

Fig.

Sep 81

Oct

• O lime

A l.25 tons lime/ha

O 2.5 tons lime/ha

Dec Jan 82

Apr

Second leaching

Second rice crop Third rice crop

2.6 The changes of the pH values in the soi l solution at 20 cm

depth of Sinacaban acid sulphate soi l during the second

leaching period and the second and third crops (treatments:

deep drainage, three lime levels) .

100 % E 8 0 - I -

6 0 - 1

40-

20-tJ/N " ' s

- /

\ s

A^

/

- / s

Ws

" s s

s ,_, s

b

k s s s

/

s s

- /

B43

- /

b/S .s

K

0

Second

20 40 60

leaching period

80 cm 0 20

Second crop

40 60 80 cm

/

/

/

S S

A.

y 0 lime

0 1.25 tons CaC03/ha

^ 2.5 tons CaC03/ha

z \1 s s s s s s s s

7

-/

'^ 0 20

Third crop

40

s s

60

s s [s

80 cm

Fig. 2.7 Frequency of occurrence of the pH of the soil solution below

3.5 at different depths in the Sinacaban acid sulphate soil

during the second leaching period and the second and third

crops (treatments: deep drainage, three lime levels).

34

EC(mS/cm) »(9.73)

4-

i — i — 1 — 1 — r -

Sep 81

I H 1 Second '

leaching

• 0 lime

A l .25 tons lime/ha

o 2.5 tons lime/ha

2.5 tons of lime/ha

Oct Dec Jan 82

Apr

Second rice crop Third rice crop

Fig. 2.8 The changes of EC values in the soil solution at 20 cm depth

of Sinacaban acid sulphate soil during the second leaching

period and the second and third crops (treatments : deep

drainage, three lime levels).

20 40 60 leaching period

H 1.25 tons lime/ha

0 2.5 tons lime/ha

\ \ \ \ \ \ \ \ \

V

\ \

\ \

\ s

/ \ \ \

/

/ .

80 cm 20 40

•y

\ \

\ \ \ \

80 cm 0

\

/ ^

J\

\ \

/ \ / \ \

\

E/^H

^

VÎ

VÏ UB^

B-

^

20 40 LI fcLbl

60 80 cm

Second crop Th i rd crop

Fig. 2.9 Frequency of occurrence of the EC values of soil solution

above 4.0 mS/cm at different depths in the Sinacaban acid

sulphate soil during the second leaching period and the

second and third crops (treatments: deep drainage, three

lime levels).

35

• 0 lime

A 1.25 tons lime/ha

O 2.5 tons lime/ha

Third rice crop

Fig. 2.10 The changes of iron concentrations in the soil solutions at

20 cm depth of Sinacaban acid sulphate soil during the sec­

ond leaching period and the second and third crops (treat­

ments: deep drainage, three lime levels).

I » 0 1.25 tons CaC03/ha

100 -

% 8 0 -

6 0 -

40-

20-

a_ä

z' \ = Vs

^

\ \ s \

Vs

\ Vs

20 40

S

\ -/,

- / . \

\

. \ \ \

Vs*

V^ \ \

80 cm ^_i£

/

\ \ \ \

\ \ \ \ \ / \

\ \

\

K \

V\

\ \ \

/

n K

%

- / /

- / /

\ Vs-

\ \ / \ \

\ \ Vs-

\ \

k - / .

Second leaching period

0 20

Second crop

40 60 80 cm 0 20

Th i rd crop

\ \ A 40

/

/

\

K 60

/ / / / / /

-/

ïïh 80 cm

2+ Fig. 2.11 Frequency of occurrence of Fe concentrations in the soi l

solution above 500 ppm at different depths in Sinacaban acid

sulphate soi l during the second leaching period and the sec­

ond and third crops (treatments: deep drainage, three lime

levels) .

36

were due to high initial EC values in the soil profile (Fig. 2.9). High

salinity gradients resulted in upward movement of ions by diffusion.

lief! 2+

Lime markedly decreased the Fe concentration in the soil solution at

20 cm depth, especially during the second leaching and the second rice 2+

crop (Fig. 2.10). There was no marked difference in Fe concentration

between treatments with 1.25 and 2.5 tons of lime/ha. During the second 2+

crop, the Fe concentration increases with proceeding duration of sub­mergence, with soluble iron levels reaching over 2000 ppm for the no

2+ lime treatment (Fig. 2.10). Even though the Fe contents were reduced

by liming, they were always higher than the toxic levels (500 mg/1 2+

soluble Fe ) as reported by Mai thi My Nhung Ponnamperuma, 1966

(Fig. 2.11), except near the soil surface.

-Aluminium

Directly after the leaching period, the aluminium concentration in the

soil solution at 20 cm depth was about 40 ppm at all three lime levels

(Fig. 2.12). During the second rice crop, lime depressed the aluminium

concentration. The aluminium concentration of the treatments with

2.5 tons of lime/ha was about 40% lower than no lime treatments during

the second crop (Fig. 2.12). As a general trend, the aluminium concen­

tration decreased with longer duration of submergence (Fig. 2.13).

During the third rice crop, a further reduction in soluble Al occurred.

* Effects of different water management practices on chemical proper­

ties of Sinacaban soil when no lime was applied

Fig. 2.14 shows the changes of pH in the soil solution at 20 cm depth

during the leaching period, and the second and third rice crops. The

highest pH values were observed in flushing treatments (above 7 ) . There

were only little differences in pH values between different drainage

treatments (Fig. 2.14), during the second crop, whereas marked differ­

ences in pH values were observed during the third crop, with deep

drainage treatment without percolation producing the lowest pH values.

37

Al3+(ppm)

120 -

80-

40

f(863) • 0 lime

A 1.25 tons lime/ha

O 2.5 tons lime/ha

£^£<^ Third rice crop

Fig. 2.12 The changes of the aluminium concentrations in the soil

solution at 20 cm depth of Sinacaban acid sulphate soil

during the second leaching period and the second and third

crops (treatments: deep drainage, three lime levels).

100 —

%

80-b

60-

40-

20-t7

0

-/

-/

•\ \ \

'X

K

&s

/ •

^ \ \

\ -/ -/ m

0 20 40 60

Second leaching period

80 cm 0 20

Second crop 40

\

_ 0 1.25 tons CaC03/ha

0 2.5 tons CaC03/ha

60 80 cm 0 20 Third crop

a^ÉS Ws

40 60 80 cm

/

3+ Fig. 2.13 Frequency of occurrence of Al concentrations in the soil

solution above 40 ppm at different depths in Sinacaban acid

sulphate soil during the second leaching period and the second

and third crops (treatments: deep drainage, three lime

levels).

38

This can be explained by a lesser pyrite oxidation with shallow drain­

age as compared to deep drainage. Percolation helped to remove some

acidity in the soil profile, resulting in higher pH values.

Regardless of water management, pH values gradually increased by flood­

ing. The highest frequencies of pH in the soil solution below 3.5, at

different soil depths, were found in deep drainage treatments without

percolation (Fig. 2.15).

-EC

An appreciable amount of salts were leached out from the profiles in

both shallow and deep drainage treatments. EC values of these treat­

ments at 20 cm depth were about 4 mS/cm as compared to 9 mS/cm for

flushing treatments at the start of the second crop (Fig. 2.16). There

was no marked change in EC values during the second crop. During the

third crop, higher EC values of the deep drainage treatment with per­

colation - as compared with the other treatments - may be due to the

upward movement of salt by diffusion from lower layers (Fig. 2.16).

This was confirmed by the higher frequency of occurrence of high val­

ues EC at 40 cm depth (Fig. 2.17). The EC values of the lower depths

remained high (Fig. 2.17).

-Fe 2 +

When the soil is kept continuously submerged (flushing treatments), the 2+

Fe concentration remains very low (Fig. 2.18). The deep drainage

treatments with percolation are taking away a large amount of iron in

the solution as compared to those without percolation. Shallow drainage

resulted in lower iron concentrations in the soil solution because of 2+

less oxidation products formed and subsequently less Fe formed during

the reduction process.

In general, the iron concentration reached its highest peak values

after 3 months of submergence during the second crop (Fig. 2.18). A

similar trend was observed during the third crop.

As the duration of submergence proceeds, the frequency of occurrence of 2+

Fe in the soil solution above 500 ppm became less at all depths in

the profile (Fig. 2.19).

pH

4-

Sep 81

39

• flushing o shallow drainage A deep drainage without percolation A deep drainage with percolation

0 ton of lime/ha

Oct

Second leaching

Second rice crop

Dec Jan 82

H h Apr

Third rice crop

Fig. 2.14 The changes of the pH values in the soil solution at 20 cm

depth of Sinacaban acid sulphate soil during the second

leaching period and the second and third crops (treatments :

0 t/ha of lime, all water management practices).

Second leaching period Second trop

[] flushing

p | shallow drainage

fj deep drainage without percolation

£j deep drainage with percolation

0 20

Third crop

Fig. 2.15 Frequency of occurrence of pH values of soil solution below

3.5 at different depths in Sinacaban acid sulphate soil

during the second leaching period and the second and third

crops (treatments: 0 t/ha of lime, all water management

practices).

EC(mS/cm)

'2 1

10

4-

2-

40

• flushing

o shallow drainage

A jeep drainage without percolation

A deep drainage with percolation

0 ton of lime/ ha

Sep 81

Oct Dec Jan 82

Second leaching

Second rice crop Third rice crop

Apr

H

Fig. 2.16 The changes of EC values in the soil solution at 20 cm depth

of Sinacaban acid sulphate soil during the second leaching

period and the second and third crops (treatments: 0 t/ha of

lime, all water management practices).

1 0 0 -

8 0 -

i 5

A :

J 20 40

Second leaching period

â

b m

^ ^

vsA

um

^

VA

A s4

\/A

'H M M

A

[ j flushing

H shallow drainage

£j deep drainage without percolation

YA deep drainage with percolation

_Q_ b^

A A A A A

40

Hi Third crop

Fig. 2.17 Frequency of occurrence of EC values of the soil solution

above 4.0 at different depths in Sinacaban acid sulphate

soil during the leaching period and the second and third

crops (treatments: 0 t/ha of lime, all watermanagement

practices).

41

• flushing O shallow drainage A deep drainage without percolation

deep drainage with percolation

0 ton of lime/ ha f f f T — •

Apr

Third rice crop

Fig. 2.18 The changes of the iron concentrations in the soil solution

at 20 cm depth of Sinacaban acid sulphate soil during the

second leaching period and the second and third crops

(treatments: 0 t/ha of lime, all water management prac­

tices) .

U flushing U shallow drainage

y deep drainage without percolation

£§ deep drainage with percolation

100 —

X

_Q_

V4

H 1 20

yt

4

/

H I

40 Second leaching period

s

o \ s

/S

'h <\

P<< y4 4

s — \ v s

H -_£•_

4 4

4

0 20

Second crop

ra

hl • s \

• 's

'4

;

2+

4

I S

0 20 Third crop

't

4 4

i l 1 ^

Fig. 2.19 Frequency of occurrence of Fe concentrations in the soil

solution above 500 ppm at different depths in Sinacaban acid

sulphate soil during the second leaching period and the

second and third crops (treatments: 0 t/ha of lime, all

water management practices).

42

Al3+(ppm)

315 863

160 H 316

120

0 J

• flushing

O shallow drainage

* deep drainage without percolation

A deep drainage with percolation

0 ton of 1ime/ha

Third rice crop

Fig. 2.20 The changes of the aluminium concentrations in the soil so­

lution at 20 cm depth of Sinacaban acid sulphate soil during

the second leaching period and the second and third crops

(treatments: 0 t/ha of lime, all water manegement prac­

tices) .

100 -

% 80-

•Ij 8

M 'ïï

H hi ^

0 20 40 Second leaching period

p

|_| flushing

M shallow drainage

— [j deep drainage without percolation

£j deep drainage with percolation

20 Second trop

SO cm 0 Third crop

Fig. 2.21 Frequency of occurrence of Al concentrations in the soil so­

lution above 40 ppm at different depths in Sinacaban acid

sulphate soil during the second leaching period and the sec­

ond and third crops (treatments: 0 t/ha of lime, all water

management practices).

-Al

43

3+

The aluminium concentration in the soil solution of the upper soil

layers decreased considerably when drainage treatments were imposed

(Fig. 2.20). Shallow drainage resulted in relatively low aluminium con­

centrations during the second crop and especially during the third

crop. During both crop growing periods deep drainage treatments with

percolation produced lower aluminium concentrations as compared to

those without drainage (Fig. 2.20). This may be explained by the re­

moval of Al-ions by the percolation.

The aluminium concentrations in the soil solution tended to decrease

during the crop growing periods.

Because of continuous submergence, a negligible amount of aluminium was

found in the flushing treatments. Fig. 2.21 shows the frequency of

occurrence of Al concentrations in the soil solution above 40 ppm at

different depths during the leaching period and the second and third

crops. As the soil underwent reduction for a longer period, the fre­

quency of occurrence of Al concentrations above 40 ppm became less.

* Effects of different water management practices at 2.5 tons/ha of

lime application on the chemical properties of Sinacaban soil

As can be expected, the pH patterns of different water management prac­

tices after application of 2.5 tons lime/ha were similar to those with­

out lime, as discussed in the preceding section.

For both shallow and deep drainage treatments, a considerable amount of

acidity was removed from the soil profile and the pH values rose 1 unit

higher than the initial values of 3.0 (Fig. 2.22). During the second

crop, the pH values of the treatments of deep drainage with and without

percolation remained low (about 4 ) , whereas the pH values of the shal­

low drainage treatment gradually increased and reached a peak value of

5.8 at the end of cropping season. The pH values of the flushing treat­

ments showed little variation and fluctuated around 7. The unexpected

low pH values of the treatment of deep drainage with percolation as

compared to those without percolation during the second crop, may be

due to soil variability and the higher acidity in the subsoil layers

44

pH

• flushing

O shallow drainage

A deep drainage without percolation

A deep drainage with percolation

2.5 tons of lime/ha

Sep 81

Oct Dec Jan 82

Apr

Second leaching

Second rice crop Third rice crop

Fig. 2.22 The changes of the pH values of the soil solutions at 20 cm

depth of Sinacaban acid sulphate soil during the leaching

period and the second and third crops (treatments: 2.5 t/ha

of lime, all water management practices).

100 —

% 8 0 -

/

> |

y

20

4

40 0

Second leaching period

8 j m dj

20

[ j flushing

|/j shallow drainage

[j deep drainage without percolation

£j deep drainage with percolation

i Second crop

0 20

Third crop

•2 40 60

Fig. 2.23 Frequency of occurrence of pH values of the soil solution

below 3.5 at different depths in Sinacaban acid sulphate

soil during the second leaching period and the second and

third crops (treatments: 2.5 t/ha of lime, all water man­

agement practices).

45

which is also reflected in higher frequency of occurrence of pH val­

ues less than 3.5 (Fig. 2.23). Except flushing treatments, the pH of

drainage treatments increased with prolonged duration of flooding dur­

ing the third crop (Fig. 2.22). With shallow drainage the peak pH value

was earlier reached than with the deep drainage treatments. The reduc­

tion processes were obviously retarded in the deep drainage treatments.

-EC

The electrical conductivity of different water management treatments

during the leaching period, and the second and third crops is shown in

Fig. 2.24. The trends are similar to those observed in the "no lime"

treatments. During the leaching period, salts were leached out by

drainage resulting in EC values dropping to less than 4 mS/cm in both

the shallow and the deep drainage treatments. Higher EC values in the

deep drainage treatments during the second crop may be associated with

the upward movement of salts from lower layers. This is reflected by

the very high frequency of occurrence of EC values above 4 mS/cm

(100 percent) in the lower depths of the profile (Fig. 2.25). No dif­

ference was found in EC values of the shallow drainage and the flushing

treatments during the third crop.

The flushing treatment had low EC values during the entire period. This

is probably due to an initial low salt content in the samples taken.

-Fe 2 +

2+ The overall trends of the Fe concentration in the soil solution were

similar to the "no lime" case. Differences were observed between the

shallow and the deep drainage treatments during the second crop

(Fig. 2.26). In the shallow drainage treatments, iron reached a peak

value of 1500 ppm after two months of flooding, whereas in deep drain­

age treatments peak values of iron of 2300 ppm occurred near the end of

the cropping season. The iron concentration remains low in flushing

treatments. During the third crop, the iron concentration in both shal­

low and deep drainage treatments increased gradually and reached their

highest values one month before harvest.

No difference in frequency of occurrence of iron above 500 ppm at 20,

40, 60 and 80 cm depths was found in the shallow and deep drainage

46

EC(mS/cm)

6-

Sep 81

Oct

Second leaching

• flushing O shallow drainage

* deep drainage without percolation

A deep drainage with percolation

Dec Jan 82

Second r i ce crop

^ ^ ^ ^ o

2.5 tons of l ime/ha T 1 1 1 1

Apr

Third rice crop

Fig. 2.24 The changes of EC values in the soil solution at 20 cm depth

of Sinacaban acid sulphate soil during the second leaching

period and the second and third crops (treatment: 2.5 t/ha

of lime, all water management practices).

100-

X

60-

40-

20 -

0 0 20 40

Second leaching period

H

I H

80 cm 0 20 Second crop

I

[ J flushing

[ j shallow drainage

[ J deep drainage without percolatio

[£j deep drainage with percolation

4

^ '•>•', 80 cm 0 20

Third crop

H

's

1 4

Fig. 2.25 Frequency of occurrence of EC values in the soil solution

above 4.0 at different depths in Sinacaban acid sulphate

soil during the second leaching period and the second and

third crops (treatments: 2.5 t/ha of lime, all water man­

agement practices).

47

Fe (ppm)

2500

2000

1500

1000

500

0

Sep 81

•

O

A

A

flushing

shallow drainage

deep drainage without percolation

deep drainage with percolation

2.5 tons of lime/ha

^7*

Oct

H—H 1 Second ' leaching

Dec Jan 82

Apr

Second rice crop Third rice crop

Fig. 2.26 The changes of the iron concentrations in the soil solution

at 20 cm depth of Sinacaban acid sulphate soil during the

second leaching period and the second and third crops

(treatments: 2.5 t/ha of lime, all water management prac-

100 —

%

8 0 -

6 0 -

4 0 -

20 —

M

'4 '4 '4 Ü

4 4

si

H 4 u

/

\

Ü

/N5;

s//

r- '

J m

4

0 20 40 Second leaching period

80 cm 0 20

Second crop

|_j flushing

M shallow drainage

[j deep drainage without percolation

£j deep drainage with percolation

J 4 4 4 4 i.2

• * • ' ,

1 80 cm 0 20

Third crop

2+ Fig. 2.27 Frequency of occurrence of Fe concentrations of the soil

solution above 500 ppm at different depths in Sinacaban acid

sulphate soil during the second leaching period and the

second and third crops (treatments: 2.5 t/ha of lime, all

water management practices).

m

48

Al3+(ppm)

120

80

40

Second leaching

• flushing O shallow drainage • deep drainage without percolation A deep drainage with percolation

2.6 tons of lime/ha

Second rice crop Third rice crop

Fig. 2.28 The changes of aluminium concentrations in the soil solu­

tions at 20 cm depth of Sinacaban acid sulphate soil during

the second leaching period and the second and third crops

(treatments: 2.5 t/ha of lime, all water management prac­

tices) .

100 —

%

8 0 -

6 0 -

a 'it A

ë /s ?

20

4

V4 hi ^

40 Ä

\ \ rA

QlbJ Second leaching period

0 20 Second crop

|_j flushing

[/] shallow drainage

[y deep drainage without percolation

^ deep drainage with percolation

80 cm 0 20 Third crop

3+ Fig. 2.29 Frequency of occurrence of Al concentrations in the soil

solution above 40 ppm at different depths in Sinacaban acid

sulphate soil during the second leaching period and the

second and third crops (treatments: 2.5 t/ha of lime, all

water management practices).

49

treatments during the second crop (Fig. 2.27). With proceeding flooding

a lower frequency of occurrence of iron above 500 ppm was observed dur­

ing the third crop.

-Al 3 +

Aluminium developed during the dry period was removed by imposing

drainage treatments. The aluminium concentration in the soil solution

of both the shallow and the deep drainage treatments dropped to about

30 ppm at the end of the leaching period and gradually decreased during

the second and third crops (Fig. 2.28). Similar to no lime application,

the frequency of occurrence of aluminium above 40 ppm was nil at 40,

60, 80 cm depths for both the shallow drainage and the flushing treat­

ments (Fig. 2.29).

* Effects of mulch during dry season on the chemical properties of

Sinacaban soil

The changes of the pH values in the soil solution at 20 cm depth below

the soil surface of the mulch and the flushing treatments during the

leaching period and the second and third crops is presented in

Fig. 2.30. pH values were higher in mulch treatments than those with­

out. Mulch reduces the soil evaporation, thus decreases the oxidation

rate, resulting in a lesser development of acidity. During the second

and third crops, the pH values were well above 4. The pH values grad­

ually increased with time in the shallow drainage treatment without

mulch for both cropping seasons. A lower frequency of occurrence of pH

values in the soil solution below 3.5 at lower depths was observed in

the mulch treatment (Fig. 2.31).

-EC

The electrical conductivity dropped to about 4 mS/cm after the flushing

and the shallow drainage were imposed (Fig. 2.32). The highest EC val­

ues were found in the shallow drainage treatments without mulch during

the second crop. This may be attributed to the upward movement of salts

from lower depths by diffusion and capillary transport with mulch sup-

pH

I — l — r

Sep 81

Oct

Second ' leaching

50

• flushing

A shallow drainage without mulch

O shallow drainage with mulch

2.5 tons of lime/ha

Dec Jan 82

Apr

Second rice crop Third rice crop

Fig. 2.30 The changes of the pH values in the soil solution at 20 cm

depth of Sinacaban acid sulphate soil during the second

leaching period and the second and third crops (treatments :

2.5 t/ha of lime, surface flushing and mulch practices).

100-

60-

40-

20-

\ \ \ \ \ \ \ \ \ \

• \

\

0 20 40

Second leaching period

\ \ \ \ \ \

60

g flushing

_ R shallow drainage with mulch

R shallow drainage without mulch

\ \

- \ \

B_N _ • 80 cm 0 20 40 60 80 cm

Second crop

0 20

Third crop

40 60 80 cm

Fig. 2.31 Frequency of occurrence of the pH values in the soil solu­

tion below 3.5 at different depths in Sinacaban acid sul­

phate soil during the leaching period and the second and

third crops (treatments: 2.5 t/ha of lime, surface flushing

and mulch practices).

51

EC(mS/cm)

6-

0J

• flushing

• shallow drainage without mulch

O shallow drainage with mulch

-O- ° o-—o- --

2.5 tons of lime/ha

Sep 81

Oct

Second leaching

Second rice crop

Dec Jan 82

-H h

Apr

Third rice crop

Fig. 2.32 The changes of EC values in the soil solution at 20 cm depth

of Sinacaban acid sulphate soil during the second leaching

period and the second and third crops (treatments: 2.5 t/ha

of lime, surface flushing and mulch practices).

Q flushing

[/] shallow drainage with mulch

k j shallow drainage without mulch

100 —

% 8 0 -

6 0 -

4 0 -

20 —

\ \ \

K t ' s

\ \

K ^

AI

FPl

\

/ \ \ \

/

\

\ \ \ \

j / \ - K N =>J

E'H

\ \ \

/ \ \ \

Vs-\ \

/ \ /

%\

\ -R/\

\ \ \ -

^ AI

• / .

\ \

\ \

y^ \ \ \ \

Vs-

-/

0 20 40 60

Second leaching period

0 20

Second crop

40 60 80 cm 0 20

Third crop

40 60 80 cm

Fig. 2.33 Frequency of occurrence of EC values in the soil solution

above 4.0 at different depths in Sinacaban acid sulphate

soil during the second leaching period and the second and

third crops (treatments: 2.5 t/ha of lime, surface flushing

and mulch practices).

52

Fe +(ppm)

1600 i

1200

800

400

Sep 81

• flushing

* shallow drainage without mulch

O shallow drainage with mulch

2.5 tons of lime/ha

Oct Dec Jan 82

Apr

Second leaching

Second rice crop Third rice crop

Fig. 2.34 The changes of iron concentrations in the soi l solution at

20 cm depth of Sinacaban acid sulphate soi l during the

second leaching period and the second and third crops

(treatments: 2.5 t /ha of lime, surface flushing and mulch

practices) .

100 —

%

8 0 -

6 0 -

4 0 -

2 0 -

\ \ \ N a \ -\ : \ :

\ =

\ :

\ =

\ \ \ \ \ \ \ \ \ \ F \ E \ \ ^ R \ \

\ \ \ \ \ \ s \ \ \ \ \ \

\ \ \

\ \ N \ \ \ \ \ \ \ \ \ \ \ ^ H

20 40 60 80 cm Second leaching period

E2J 0 20

Second crop

\ \ \ \ \ \ \ \ \ \ \

F^ t \ \

\ \ \ \ \ \ \ s \ \ \ \ \ \ b

\ z \

\ \ \

z \ 3_L 40 60

g flushing

[/] shallow drainage with mulch

^j shallow drainage without mulch

80 cm

z

\ \ \ \ \ \ \ \ \ \ \

\ -\ z \ F \ \ t \ ~ \ z \ -

N \ \ \ \ \ \ \ \ \

\ 1̂ \

\ -H \ - \

0 20

Third crop 40 60 80 cm

2+ Fig. 2.35 Frequency of occurrence of the Fe concentrations in the

soil solution above 500 ppm at different depths in Sinaca­

ban acid sulphate soil during the second leaching period and

the second and third crops (treatments: 2.5 t/ha of lime,

surface flushing and mulch practices).

53

pressing the latter. The frequency of occurrence of EC values lower

than 4 mS/cm at 40 cm depth in the shallow drainage treatments with

mulch was 50 percent as compared to 78 percent of those without mulch

(Fig. 2.33).

-Fe 2 +

Mulch markedly influenced the iron concentration in the soil solution

at 20 cm depth below the soil surface (Fig. 2.34). The average iron

concentrations of the mulch treatments during the second crop was about

200 ppm as compared to 1000 ppm of the no mulch treatments. Lower iron

concentration in mulch treatments was attributed to smaller amounts of

oxidation products. This coincides with the lower frequency of occur­

rence of iron in the soil solution above 500 ppm at different depths in

the shallow drainage treatment with mulch (Fig. 2.35). There was only a

slight variation of iron concentrations with time in both the flushing

and the shallow drainage treatments with mulch (Fig. 2.34).

-Al 3 +

The shallow drainage treatment without mulch produced large amount of

aluminium during the dry season (Fig. 2.36). The aluminium together

with other ions were removed from the soil profile when the drainage

treatments were imposed.

Drainage without mulch brought down aluminium concentration to about

30 ppm at the end of the leaching period (Fig. 2.36). Shallow drainage

with mulch and the flushing caused similar aluminium concentration pat­

terns during the leaching period, and the second and third crops

(Fig. 2.36).

Because the soil at lower depths (> 40 cm) was kept saturated with

water during the experiment, no oxidation took place, and the frequency

of occurrence of Al above 40 ppm in both drainage treatments was nil

(Fig. 2.37).

54

Al3+(ppm)

I T 4(292)

120

80

40

0 J

• flushing

A shallow drainage without mulch

O shallow drainage with mulch

2.5 tons of lime/ha

Third rice crop

Fig. 2.36 The changes of the aluminium concentrations in the soil so­

lution at 20 cm depth of Sinacaban acid sulphate soil during

the second leaching period and the second and third crops

(treatments: 2.5 t/ha of lime, surface flushing and mulch

practices).

60-

% 40-

20-

\ \ \ \ \ \

\ \ \ \ \

K

\ \ \ \ \ \ N

\

\ \ \ \ N

\ \ \ \ \ \ \ 20 40 60

Second leaching period

i_Jl

y flushing

— [/J shallow drainage with mulch

KJ shallow drainage without mulch

80 cm 0 20 40 Second crop

60

,3+

80 cm 0 20 Third crop

40 60 80 cm

Fig. 2.37 Frequency of occurrence of Al~" concentrations in the soi l

solution above 40 ppm at different depths in Sinacaban acid

sulphate soi l during the second leaching period and the

second and third crops (treatments: 2.5 t /ha of lime, sur­

face flushing and mulch pract ices) .

55

General discussion on chemical properties of Sinacaban acid sulphate

soil

Although there are some variabilities of the chemical properties within

the same treatment, the following points related to the influence of

agronomic and water management practices on the chemical properties of

the soil solutions can be summarized:

- Lime has markedly decreased the iron and aluminium concentrations in

the soil solution at 20 cm depth at deep drainage treatments during

the second and third crops. It had no detectable influence on pH.

With deep drainage of this soil, pH drops to a very low value and 2+ 3+

produces a large amounts of Fe and Al as compared to the shallow

drainage. The reduction processes during the following cropping

seasons were retarded in the deep drainage treatments.

- Mulching with 5 cm of rice straw minimizes the water loss by evapo­

ration, and reduces the oxidation rate. This results in a lesser 2+ 3+

development of acidity and less Fe and Al products.

- When the soil is continuously flooded with water, no pyrite is oxi-2+ 3+

dized resulting in low acidity and low Fe and Al

2.3.5 Effects of water management and agronomic packages on the

grain yield of rice in two acid sulphate soils

The grain yields of the three rice crops in both soils are presented in

Tables 2.10, 2.11 and 2.12. Because statistical tests of significance

cannot be adequately based on two replicates only, values of each

replicate and means are presented to indicate the results of this ex­

periment. Grain yield data of different treatments are given separately

for various treatments, e.g. drainage, liming and agronomic packages.

Obviously, grain yields differed greatly among the two soils and three

cropping seasons.

56

Table 2.10 Grain yield of rice in two acid sulphate soils, wet season,

1980 (first crop) for each of the treatments applied.

Treatment

1

2

3

4

5

6

7

8

9

10

11

Ap arri soi

Replicate

1

148.5

145.3

110.8

162.4

128.2

131.0

134.1

133.7

138.5

155.2

135.5

2

164.4

161.9

126.8

143.5

151.1

202.0

163.0

138.8

150.4

Grain yield (g/drum)

1

Average

156.4

153.6

118.8

152.9

139.7

166.5

148.5

136.2

144.5 21

155.2 '

135.52)

Sinacaban

Repl

1

155.7

126.3

136.5

105.6

130.7

144.3

155.1

0.0

138.5

58.5

134.1

icate

2

160.5

132.3

152.5

129.7

172.6

164.9

159.8

64.0

159.3

soil

Average

158.1

129.3

144.5

117.6

151.6

154.6

157.4

32.0

148.9

58.52)

134.12)

1) Average of two replicates

2) Only one yield replicate available

2.3.5.1 Aparri acid sulphate soil

The grain yield varied with the cropping season (Tables 2.10, 2.11 and

2.12). As expected, the grain yields of different treatments in the

first cropping season showed little variation (Table 2.10), because

the soil was continuously kept at water saturation and no acidification

took place. Contrary to expectation, however, there was also no marked

effect of drainage, lime application or agronomic practice on grain

yield in the second and the third crop (Table 2.11 and 2.12).

Before transplanting the second and third crops, the pH value of the

57

Table 2.11 Grain yield of rice in two acid sulphate soils, dry season,

1981 (second crop) for each of the treatments applied.

Treatment

1

2

3

4

5

6

7

8

9

10

11

Ap

Repli

1

91.9

105.7

136.0

87.6

97.9

106.4

92.8

88.2

118.4

83.5

141.5

arri soi

cate

2

105.8

24.5

144.0

132.4

109.0

140.8

127.2

146.4

118.8

Grain yield

1

Average

98.9

115.1

140.0

110.0

103.4

123.6

110.0

117.3

118.6

83.52)

141.52)

(g/drum)

Sinacaban

Replicate

1

0.0

0.0

0.0

0.0

0.0

0.0

34.7

68.7

93.4

90.0

0.8

2

12.2

0.0

0.0

0.0

0.0

102.8

95.3

109.0

118.3

soil

Average

6.1

0.0

0.0

0.0

0.0

51.4

65.0

88.9

105.9

90.02)

0.82)

1) Average of two replicates

2) Only one yield replicate available

soil solution in the surface soil was well above 5.0, regardless of

treatment. The relatively high pH value (Table 2.6) and the low values

of dissolved iron in the surface soil layer (less than 100 ppm) indi­

cated that Aparri soil was not influenced by pyrite oxidation during

the dry period. This was confirmed by the pH values of the pyritic sub­

stratum which also stayed rather constant through drainage periods.

Apparently, soil acidity in this soil is not severe enough to hamper

the growth of rice. Indeed, draining the soil did not affect the grain

yield. This confirms the earlier conclusion that Aparri is not a prob­

lem soil.

58

Table 2.12 Grain yield of rice in two acid sulphate soils, dry season,

1982 (third crop) for each of the treatments applied.

Treatment

1

2

3

4

5

6

7

8

9

10

11

Aparri soi

Repl

1

289.4

316.6

298.6

289.9

252.1

280.9

271.4

266.4

287.8

270.7

283.9

cate

2

320.1

342.5

340.7

322.9

334.7

289.2

348.5

295.08

343.0

Grain yield

1

Average

304.8

329.5

319.6

306.4

293.4

285.0

309.9

281.1

315.4

270.72)

283.92)

(g/drum)

Sinacaban

Repli

1

0.0

0.0

1.2

198.8

0.0

0.0

202.8

275.6

322.2

234.4

292.5

cate

2

196.0

0.0

125.0

338.3

92.2

346.4

319.9

293.2

359.7

soil

Average

98.0

0.0

63.1

268.6

46.1

173.2

261.4

284.4

341.0

234.42)

292.52)

1) Average of two replicates

2) Only one yield replicate available

2.3.5.2 Sinacaban acid sulphate soil

* First cropping season

After the installation of the various instruments in the drums, the

various treatments were applied and IR 36 was transplanted. During this

season the soils did not undergo a drying treatment, so the oxidation

was minimal (Table 2.7). As a result the grain yields (Table 2.10) were

hardly affected by treatments, except in one lysimeter (8.) which had

leaked during transportation, causing pyrite oxidation and producing a

large amount of acidity which was not leached out sufficiently. Plants

59

in this lysimeter therefore suffered from severe stresses: low pH, high

Al and Fe concentrations and died after some weeks.

* Second and third cropping seasons

In the following sections, the effects of drainage, lime and agronomic

practices will be presented and discussed.

. Effects of water management treatments at zero lime

The influence of different water managements at zero lime on the grain

yield of rice is presented in Fig. 2.38. The grain yield in drums with

the deep drainage treatment was poorest in both the second and the

third season (Fig. 2.38). The highest yields were obtained with the

flushing treatment, the next highest with shallow drainage. Grain

yields of the third crop were considerably higher than those of the

second crop. The differences can be ascribed in part to more favour­

able soil conditions during the third crop: toxic elements were partly

removed by leaching in the previous drainage period and by reduction

processes during the second crop. The depression of the grain yields in 2+

the deep drainage treatment was associated with high acidity, high Fe

concentration and low pH values in the soil solution (Fig. 2.14 and

2.18).

• Influence of flushing

The grain yields in the flushing treatments were superior to those in

the deep and the shallow drainage treatments, both in unlimed and in

limed soils (Fig. 2.38 and 2.39). The yields of the third crop were

about 300 percent higher for the flushing, the shallow and the deep

drainage treatments, respectively, compared to the second crop.

. Influence of percolation on the grain yield of the deep drainage

treatments

Contrary to expectation, the grain yields in the deep drainage treat­

ment were lower with percolation as compared to without at 2.5 tons

of lime/ha (Fig. 39). This can be explained by incomplete removal of

acidity and by soil variability.

With deeper drainage, the contact between soil and air increases, and

60

H

^

H \*>%

• I

H,

m m «b >

«

•H U

S 3

61

oxidation and acidification intensify. Because the acidity developed

during oxidation was not sufficiently removed by leaching, or was neu­

tralized by liming, oxidation due to deep drainage had detrimental ef-2+

fects to rice plant. Upward diffusion of Fe to the surface water fol-2+

lowed by oxidation of Fe to ferric hydroxide, produced appreciable

amounts of acidity in the surface water. The acidity gradient between

the surface water and the soil solution of the upper soil layers may

cause a downward movement of acidity to the surficial roots of young

rice plants. This high acidity hampered the root development and as a

result the growth of rice was retarded.

• Influence of lime levels in the deep drainage treatments

The rice of the second crop failed completely, both at the application

of 0 and of 1.25 tons of lime/ha, due to the excess acidity (Fig.

2.40). Only after increasing the amount of lime up to 2.5 tons/ha, the

rice produced some yield, due to the decreased acidity. In the third

crop, the soil toxicity had apparently been decreased so much by leach­

ing and chemical reduction that also at a low dose of lime, the rice

yielded about 40 g/ drum. The acidity remained very high in the treat­

ment without lime (Fig. 2.6).

. Influence of mulch on the grain yields of rice at an application of

2.5 t/ha of lime

The influence of mulch on the grain yield of the second and third sea­

son was clear (Fig. 2.41). Mulching increased grain yield of the second

and third crops with 67 and 30 percent, respectively. Mulch helped to

conserve moisture in the profile (Table 2.5), to minimize pyrite oxida­

tion and to produce less acidity. The differences in grain yields of

the two cropping seasons may be due to the differences in chemical

properties of the soil and to climatological factors. The results of

this experiment indicate that mulching is a promising treatment for

this soil.

62

. Occurrence frequency of successful crops under different water

management practices

The results of the experiment with different water management prac­

tices of the Sinacaban soil on the grain yield may be illustrated by

showing the frequency of successful crops. A "successful crop" is de­

fined in our case as a crop with a yield of at least 1 ton/ha or 60 g/

lysimeter. For example, if three out of the four replicates gave more

than 60 g per drum, the frequency of successful crops was indicated as

75%. Irrespective of the lime levels, the crops were 100% successful

after flushing (Fig. 2.42). This success is not dependent on lime ap­

plication. At zero lime level, the crops were found to be 50% and 0%

successful after the shallow and the deep drainage treatments, respec­

tively. Increasing lime levels from 1.25 to 2.5 tons/ha increased the

frequency of successful crops for both levels after the shallow and the

deep drainage. The deep drainage treatment was generally the least suc­

cessful revealing the hazardous nature of this treatment. The acidity,

developed in the deep drainage treatment could only be removed with

large amounts of water for leaching.

The data presented in Figure 2.42 are indicative rather than conclu­

sive; the danger of deep drainage should be taken into account in

100

50 — I I

I J d&

^

D Second crop

Third crop

Fig. 2.42 Occurrence frequency of successful crops under different

water management practices for the second and third crops

in Sinacaban acid sulphate soil.

63

planning any reclamation project, where water or time is a limiting

resource. In the case of potential acid sulphate soil, prevention is

better than curative treatment.

. Grain yield in relation to chemical changes of stagnant surface water

and of the soil solution of the surface soil

Water management and agronomic practices influence the chemical status

of the acid or potential acid sulphate soils. The chemical status of

the soil in turn influences the performance of rice. So far, no model

is available, which relates grain yield and condition of the soil solu­

tion during the crop growth period. A pH value as low as 3.5 did not,

by itself, have a harmful effect to rice (Thawornwong and van Diest,

1974; Le ngoc Sen, 1982b). Iron concentrations in the soil solution

higher than 500 ppm are toxic (Mai thi My Nhung and Ponnamperuma, 1966)

and aluminium of 20-40 ppm caused aluminium toxicity. Based on these

known threshold values, a combined effect of these factors was used to

correlate with the grain yields. A score of 1 was set separately for pH

between 3 and 3.5, dissolved iron greater than 500 ppm and for alumi­

nium concentrations greater than 30 ppm for each observation during the

growth period. Otherwise a zero-score was assigned. The total number of

scores was then divided by the number of observations. The average of

the three ratios, expressed as percentage, is called the average min­

eral stress index (AMSI). If pH of the surface water was less than 3,

the AMSI was set to 100%. This index is then used to correlate with the

logarithm of the grain yields. Data from Mai thi My Nhung and Ponnam­

peruma (1966) were used to correlate the logarithm of grain yields and

AMSI calculated by method mentioned above. This graph showed a linear

correlation (Fig. 2.43).

The correlation between the logarithmic grain yields and average min­

eral stress index for the second and third crops in Sinacaban acid sul­

phate soil are presented in Fig. 2.44. In the second crop two distinct

regions could be distinguished: at AMSI less than 40% the grain yields

ranged from 20 to 90 g per drum, and if AMSI equals 100%, the grain

yields were always zero. There was no correlation between grain yields

and AMSI at lower AMSI values, which may be due to other factors such

as salinity or microclimate.

64

o

o e>

«

*o

o

-^-•«BO 'O ' L-

O • O

•

• •

O

• •

—%-•—'

•

1 1 1 1 I 1

•

1 1

CL o u o • o c o L> <U

X

1

CL O Î-u

l~

1—

I

^

s 1

• i

1

<*

* ~

-

— J l

3 *

65

2.4 Summary and conclusions

The influence of different agronomic and water management practices on

the growth of rice and on the chemical changes of Aparri and Sinacaban

acid sulphate soils were studied in forty undisturbed soil cores (60 cm

diameter, 90 cm deep) subjected to different water management prac­

tices, liming rates and mulch application for two leaching periods and

three rice crops. IR36 rice variety was transplanted. Surface water and

soil solutions at 20, 40, 60 and 80 cm depths were collected for pH, 2+ 3+

EC, Fe and Al determination.

There was a great difference in chemical properties and grain yield of

the two soils.

In Aparri soil, there was no marked effect of drainage, liming and

agronomic practices on the chemical properties of the soil solution

during the two leaching periods and during the three rice crops. These

associated with the well developed and mature surface soil and the

minimal pyrite oxidation in the subsoil. The grain yields of the three

crops were high and were not influenced by different treatments.

In Sinacaban soil, however, the effects of drainage, liming and agron­

omic practices on the chemical properties of the soil solutions were

very pronounced. Imposing deep drainage to the soil created favourable

conditions for pyrite oxidation, which resulted in high acidity produc-

2+ 3+ tion and higher Fe and Al . The frequency of occurrence of pH val­ues less than 3.5 was 100 percent in the subsoil layers below 40 cm.

Shallow drainage did not cause severe oxidation in the subsoil layers 2+ 3+

and produced less acids and lower Fe , AI concentrations. Shallow

drainage in combination with a mulch application (5 cm of rice straw)

minimized water loss from the soil, and hindered oxygen movement to the 2+ 3+

subsoil. This resulted in less acid development and lower Fe , AI

concentrations. When the soil was continuously submerged, no pyrite 2+ 3+

oxidation took place, nor any production of Fe and Al ions. The

reduction process followed the same trend as in other experiments from

surface materials of acid sulphate soils reported by Mai thi My Nhung

and Ponnamperuma (1966). Even with prolonged submergence, reduction was 2+

very slow in the subsoil layers. The acidity and the Fe concentration

66

remained very high for a long period (9 months). The aluminium concen­

tration decreased with increasing pH-values of the soil.

In Sinacaban soil, during the first cropping season, grain yields were

hardly affected by treatments, because the soils did not undergo a dry­

ing period. During the second and third cropping seasons, the influence

of different treatments on grain yields was very pronounced. The deep

drainage treatment gave the poorest yields of both the second and third

crops. Highest yields were obtained with the surface flushing treat­

ment, the next highest yields with the shallow drainage. Irrespective

of lime levels, the grain yield in the deep drainage treatments was

lower with percolation than without. Mulching increased the grain

yields of the second and third crops by 67 and 30 percent, respective­

ly. In the deep drainage treatment, only high amounts of lime,

2.5 tons/ha, produced a yield exceeding the equivalent of about 1 t/ha.

The frequency of occurrence of "successful crops" under different prac­

tices revealed the superiority of the flushing treatment. The concept

of the average mineral stress index (AMSI) was introduced to correlate 2+

grain yield and toxic elements in acid sulphate soils (pH, Fe and 3+

Al ) , but the correlation was less pronounced than that obtained from

results found by Mai thi My Nhung and Ponnamperuma (1966).

The provisional management measures to increase rice production in acid

sulphate soils areas are the following: Well developed, mature acid

sulphate soils with a pyritic layer deeper than 40 cm (sulphic Tropa-

quept of the Aparri type), are hardly subject to acidification, even

when the ground water table is lowered to 80 cm below soil surface.

Therefore attention should be focused on the source of water for wash­

ing out the excess salt (if the soil is saline) and on the fertiliza­

tion practices.

The potential acid sulphate soils of Sinacaban type will produce a

large amount of acids upon drainage. Reclamation measures are therefore

largely dependent on the water availability. In areas with sufficient

water, the soil should be kept continuously flooded and in areas, where

water is scarce during some parts of the year, shallow drainage in com­

bination with mulch is most likely to reduce the problems.

67

2.5 References

Abichandani, CT., and S. Patrick, 1955. Mineralizing action of lime on

soil nitrogen in water-logged rice soils. Rice Comm. Newsl. 13:

11-13.

Abichandani, C.T. and R.S. Patrick, 1961. Effects of lime application

on nitrogen availability and rice yields in water-logged soils. In­

dian Soc. Soil Sei. 9: 55-62.

Aimi, R. , T. Murakami, 1964. Cell physiology studies on the effects of

aluminium on the growth of crop plants. Bull. Nat. Inst. Agr. Sei.

Japan. Dil, 331.

Annual Report WARRS, 1959. West Afr. Rice Res. Sta., Rokupr. Sierra

Leone, Annu. Rep. p. 32.

Arnon, D.I. and CM. Johnson, 1942. Influence on hydrogen-ion concen­

tration on the growth of higher plants under controlled conditions.

Plant Physiology 17: 525-539.

Arnon, D.I., W.E. Fratzke, and CM. Johnson, 1942. Hydrogen-ion concen­

trations in relation to absorption of inorganic nutrients by higher

plants. Plant Physiology 17: 515-524.

Aslander, A., 1952. Standard fertilization and liming as factors in

maintaining soil productivity. Soil Sei. 74(3): 181-195.

Attandana, R., 1971. Amelioration of an acid sulphate soil. Unpublished

M.S. thesis. UPLB, Los Banos, Laguna, Philippines.

Ayotade, K.A., 1977. Kinetics and reactions of hydrogen sulfide in so­

lution of flooded rice soils. Plant and Soil 46: 381-389.

Baba, I., K. Inada and K. Tajima, 1964. Mineral nutrion and occurrence

of physiological diseases. In: Mineral nutrition of the Rice Plant.

The John Hopkins Press, Baltimore, Maryland, U.S.A. pp. 173-195.

Bannink, D.W., P. Poelstra and M.J. Frissel, 1977. An installation for

transport and accumulation studies on undisturbed soil columns under

controlled conditions. Netherlands J. Agric. Sei. 25: 126-135.

Begheijn, L.Th., N. van Breemen and E.J. Welthorst, 1978. Analysis of

sulphur compounds in acid sulphate soils and other present marine

soils. Soil Sei. and Plant Analysis 9 (9): 873-882.

Beye, G. , 1973. Acidification of mangrove soils after empoldering in

Lower Casamanse. Effects of the type of reclamation system use. In

68

H. Dost (ed.)- Acid sulphate soils. Proc. Int. Symp. Wageningen, ILRI

Publ. 18. Vol. II: 359-371.

Black, C.A., 1968. Soil-plant relationship, 2nd edition. John Wiley and

Son, Inc. New York, 792 pp.

Black, C.A. and C.A.J. Goling, 1953. Organic phosphorus in soils. In:

Soil and Fertilizer phosphorus. Pierre, W.H. and A.G. Morman, eds.

Agron. 4: 123-152.

Black, CA., D.D. Evans, J.L. White, L.E. Ensminger and F.E. Clark,

1965. Methods of soil analysis. Part 2: Chemical and Microbiological

properties. American Society of Agronomy, Inc., Publisher, Madison,

Winconsin, pp. 1572.

Black, J.H. and M.G. Raines, 1978. Soil sampler with retrievable liner.

J. Soil Sei. 29: 271-276.

Blair, A.W. and A.L. Prince, 1927. The relation of soil reaction to

active aluminum. Soil Sei. 24: 205-213.

Bloomfield, C , J.K. Coulter, R. Karis-Sotirion, 1968. Oil palms on

acid sulphate soil in Malaya Trop. Agric. (Trin.) 45: 289-300.

Bloomfield, C , and J.K. Coulter, 1973. Genesis and management of acid

sulphate soils. Adv. Agron. 25: 265-236.

Borthakur, H.P., and N.N. Mazumder, 1968. Effect of lime on nitrogen

availability in paddy soil. Indian Soc. Soil Sei. 16: 143-147.

Bower, C.A. and J.T. Hardier, 1970. Reclamation of acid sulphate soils

by leaching with sea water. Int. Rice Comm. Working Party on Rice

Soils, Water and Fertilizers Practices No. 9-13.

Cate, R.B. Jr. and A.P. Sukhai, 1964. A study of aluminium in rice

soils. Soil Sei. 98: 85-93.

Chang, S.C, and Y.S. Puh, 1951. An investigation on lime requirements

for rice on acid soil in Taiwan (2). Agr. Res. 2(1): 1-31.

Cole, C.V. and M.L. Jackson, 1950. Solubility equilibrium constant of

dihydroxy aluminum dihydrogen phosphate relating to mechanism of

phosphate fixation in soils. Proc. Soil Sei. Soc. Amer. 15: 84-88.

Coleman, N.T., E.J. Kamprath and S.B. Weed, 1958. Liming. Adv. in

Agron. 10: 475-522.

Craswell, E.T. and E.G. Castillo, 1979. A convenient device for taking

large undisturbed samples of paddy soil. International Rice Res.

Newsl. 4(4): 22.

69

Driessen, P.M. and Ismangun, 1973. Pyrite containing sediments of

Southern Kalimantan, Indonesia: their soils, management and reclama­

tion. In: H. Dost (ed.). Acid sulphate soils. Proc. Int. Symp. Wage­

ningen, IRRI, Publ. 18 Vol. II: 345-348.

Evans, H. and R.B. Cate, 1962. Studies in the improvement of problem

soils in British Guiana. World Crops 14: 370-373.

Fleming, J.F., L.T. Alexander, 1961. Sulphur acidity in South Carolina.

Tidal Marsh Soils. Proc. Soil. Sei. Soc. Amer. 25: 94-95.

Ha, H.S., 1970. Studies on acid sulphate soils. Effect of the rice

plant growth by amount of lime application on no percolation and

percolation. J. Korean Soc. Soil Fert. 3: 29-34.

Hart, M.G.R., A.J. Carpenter and J.W.O. Jeffrey, 1963. Problems in

reclaiming saline mangrove soils in Sierra Leone. Agron. Trop.

(Paris) 18: 800-802.

Hesse, P.R., 1961. The decomposition of organic matter in a mangrove

Swamp soil. Plant and Soil 14(3): 249-263.

Inada, K., 1965. Studies on bronzing diseases of rice plant in Ceylon.

2. Cause of the occurrence of bronzing. Crop. Sei. Soc. of Japan

Proc. 33: 315-323.

IRRI, 1963. Annual Report 1963. Int.

Laguna, Philippines.

IRRI, 1964. Annual Report 1964. Int.

Laguna, Phi1ipp ine s.

IRRI, 1965. Annual Report 1965. Int.

Laguna, Philippines.

IRRI, 1967. Annual Report 1967. Int. Rice Res.

Laguna, Philippines.

Islam, A. and Shah Mohammad Ullah, 1968. Reclamation of Kosh Soil.

Pakistan J. Soil Sei. 4: 45-53.

Iwaki, S., K. Ofa and T. Ogo, 1953. Studies on salt injury in the rice

plant: IV (English Summary of Japanese). Proc. Crop. Sei. Soc. Japan,

22: 13-14.

Iwaki, S., 1956. Studies on the salt injury in rice plant. Elsime Univ.

Men. Sect. VI Vol. II (1) (In Japanese and English summary): 141-149.

Kaberathuman, S. and S. Patnaik, 1978. Effects of submergence on the

availability of toxic and deficient nutrients in acid sulphate soils

Rice Res. Inst., Los Banos,

Rice Res. Inst., Los Banos,

Rice Res. Inst.

Inst.

Los Banos,

Los Banos,

70

of Kerala. Agr. Res. J. Kerala, 1978. 16(2): 181-187.

Kanarengsa, Chob and Yaovapa Chantraragul, 1972. Liming effects on the

growth and yield of rice in combination with various rates of ni­

trogen and phosphate. Annual Report on Rice Fertilization experiment

for 1971. Soil Fertility Branch, Technical Division, Rice Department,

Ministry of Agriculture, Thailand.

Kawalec, A., 1973. Word distribution of acid sulphate soils. References

and Map. In: H. Dost (ed.). Acid sulphate soils. Proc. Int. Symp.

Wageningen, ILRI Pub. 18. Vol I: 293-295.

Kawaguchi, K. and K. Kyuma, 1969. Lowland rice soils in Thailand. Re­

ports on Reseach in Southeast Asia. Natural Science. Monograph Series

No. 4.

Kevie, W. van der, 1972. Morphology, genesis occurrence and agricul­

tural potential of acid sulphate soils in Central Thailand. Thai. J.

Agric. Sei. 5: 165-182.

Kivinen, E. , 1950. Sulphate soils and their management in Finland.

Trans. Int. Congr. Soil. Sei. 4th 1950 Vol. 2: 259-262.

Kittrick, J.A. and M.L. Jackson, 1955. Rate of phosphate reaction with

soil minerals and electron microscope observation and on the reaction

mechanism. Proc. Soil Sei. Soc. Amer. 19: 292-295.

Khallik, O.G., 1959. Effect of liming on the fertility of acid soils in

Estonian SSR. Soviet Soil. Sei. 10: 1172-1176.

Koshy, M.M. and A.P.A. Bito-Mutunayagam, 1961. Fixation and avail­

ability of phosphorus in soils of Kerala. Agr. Res. Journ. of Kerala.

1: 70-78.

Le ngoc Sen, 1982a. A simple low-cost method to collect undisturbed

cores of acid sulphate soil profiles for the study of water and

solute movement during reclamation and use for wet land rice. In:

H. Dost (ed.). Acid sulphate soils. Proc. Int. Symp. Wageningen,

ILRI, Pub. 31. pp. 381-388.

Le ngoc Sen, 1982b. The effects of acid sulphate flood water on the

growth of rice and on the chemical changes in three acid sulphate

soils. In: Proceedings of the International Symposium on Soil,

Geology and Landforras: Impact on Land use planning in developing

countries, April 1982, Bangkok, Thailand. A17: 1-30.

71

Lockard, R.G., 1956. Research on penyakit merah in Malaysia. Int. Rice

Coram. Newsl. No. 18: 12-16.

Mai thi My Nhung, Ponnamperuna, F.N., 1966. Effects of calcium car­

bonate, manganese dioxide, ferric hydroxide and prolonged flooding on

chemical and electrochemical changes and growth of rice in a flooded

acid sulphate soil. Soil Sei. 102: 29-41.

Matsuguchi, T. et al., 1970. Non symbiotic nitrogen-fixing micro­

organisms and nitrogen fixation in paddy soils in Thailand. The

report of the joint research work between Japan and Thailand. Trop­

ical Agriculture Research Center, Ministry of Agriculture and For­

estry, Japan.

McLean, E.O., W.R. Honrigon, H.E. Shoemarker and D.R. Bhumbla, 1964.

Aluminum in soils: V. Form of aluminum as a cause of soil acidity and

a complication in its measurement. Soil Sei. 97: 119-126.

Mehlich, A., 1946. Soil properties affecting the proportionate amount

of calcium, magnesium and potassium in plants and in HCl extracts.

Soil Sei. 62: 393-409.

Mielke, L.N., 1973. Encasing undisturbed soil cores in plastic. Proc.

Soil Sei. Soc. Amer. Proc. 37: 325-326.

Mitsui, S., S. Aso and K. Kumazawa, 1951. Dynamics studies on the

nutrient uptake by crop plants. The nutrient uptake of rice roots as

influenced by hydrogen sulfide. J. Sei. Soil Manure, Japan, 22:

46-52.

Miyake, K. , 1916. Toxic action of soluble aluminium salt upon the

growth of rice plant. J. Biol. Chem. 25: 23-28.

Moormann, F.R., 1961. Acid sulphate soils of the tropics. Research on

acid sulphate soils and their amelioration by liming. Agronomic

library, Vietnam Soil Service. 82pp.

Mulleriyawa, R.P., 1966. Some factors influencing bronzing. A physio­

logical disease of rice in Ceylon. M.S. thesis, University of the

Philippines, College of Agriculture.

Nagata, T., 1953. Aluminium uptake by tomato plant. J. Sei. Soil Ma­

nure, Japan, 24: 255-221.

Nambiar, E.P., 1961. Influence of liming on the biological activity in

the soil. Agr. Res. Jour, of Kerala 1(1): 95-98.

72

Nomoto, K. and P. Kisida, 1959. Some problems of fertilization on the

acid soil. IV. Influence of aluminium absorbed in crop plants on the

movements of phosphorus. Bull. Tokai Kinki Nat. Agr. Exp. St. 2nd

Agronomy Division 1, 45.

Park, N.J., Y.S. Park and Y.S. Kim, 1971. Effect of lime on growth of 2+

rice and changes in pH, Fe and Al in an acid sulphate. Soil. J.

Korean Soc. Soil Sei. Fert. 4: 167-175.

Park, N.J., Y.S. Park, K.H. Lee and Y.S. Kim, 1972. The effect of lime

and wollastonite on an acid sulphate soil. J. Korean Soc. Soil Fert.

5: 25-32.

Pearson, G.A., 1959. Factors influencing salinity of submerged soils

and growth of caloro rice. Soil Sei. 87: 198-206.

Pearson, G.A., 1961. The salt tolerance of rice. Int. Rice Comm. Newsl.

10: 1-4.

Perkins, A.T. and H.H. King, 1944. Phosphate fixation by soil minerals

II. Fixation by iron, silicon and titanium oxides. Soil Sei. 58:

243-250.

Pierre, W.H., 1938. Phosphorus deficiency acid soil fertility. USDA

Agricultural Year Book, 1938. pp. 377-396.

Pham huu Ann, F.R. Moorman and J.D. Golden, 1961. Liming experiments on

acid sulphate soils. In: Researches on acid sulphate soils and their

amelioration by liming. Ministry of Rural Affair, Vietnam, pp. 19-52.

Ponnamperuma, F.N., R. Bradfield, M. Peech, 1955. A physiological dis­

order of rice attributable to iron toxicity. Nature 175: 265.

Ponnamperuma, F.N., 1958. Lime as a remedy for a physiological disease

of rice associated with excess iron. Int. Rice Comm. Newsl. 7(1):

10-13.

Ponnamperuma, F.N., 1960. The benefits of liming acid lateritic rice

soils of Ceylon. 7th Int. Congress of Soil Science. Madison, Wise.

U.S.A.

Ponnamperuma, F.N., 1964. Dynamic aspects of flooded soils and the

nutrition of the rice plant. In: Proc. Symp. Mineral Nutr. Rice

Plant, Maryland, U.S.A. John Hopkins Press. 494 pp.

Ponnamperuma, F.N., Wen Lin Yuang and Mai thi My Nhung, 1965. Manganese

dioxide as a remedy for a physiological disease of rice associated

with reduction of the soil. Nature 207: 1103-1104.

73

Ponnamperuma, F.N., T. Attanandana and G. Beye, 1973. Amelioration of

three acid sulphate soils for lowland rice. In: H. Dost (ed.). Acid

sulphate soils. Proc. Int. Symp. Wageningen, ILRI Pub. 18, vol. II:

391-406.

Pons, L.J., Zonneveld, I., 1965. Soil ripening and soil classification.

ILRI Pub. 13, Veenman, Wageningen. 128 pp.

Richards, L.A., 1954. Diagnosis and improvement of saline and alkaline

soils. U.S. Dept. of Agr. Handbook 60, 160 pp.

Richmond, T. de A., J. Williams and V. Datt, 1975. Influence of drain­

age on pH, sulphate content and mechanical strength of a potential

acid sulphate soil in Fijii. Trop. Agric. (Trinidad) 52: 325-334.

Rorison, I.H., 1973. The effect of extreme soil acidity on the nutrient

uptake and physiology of plant. In: H. Dost (ed.). Acid Sulphate

Soils, Proc. Int. Symp. Wageningen, ILRI Pub. 18, vol. I: 223-254.

Sahrawat, K.L., 1979. Iron toxicity to rice in an acid sulphate soil as

influenced by water regimes. Plant and Soil 51: 145-151.

Sombatpanit, S. and L. Wangpaiboom, 1973. Study on the lime require­

ments of an aluminum rich acid sulphate soil. Paper presented at

Twelfth Conf. Agric. Biol. Sei. Kasetsart University, Bangkok,

Thailand.

Sombatpanit, S., 1975. Improvement of acid sulphate soil in Thailand.

Int. Rice Res. Conf. 1975. Conbrib. 263 pp.

Struthers, P.H. and D.H. Sieling, 1950. Effect of organic anions on

phosphate precipitations by iron and aluminum as influenced by pH.

Soil Sei. 69: 205-213.

Subramoney, N. and T.K. Balakrishmakurup, 1961. A physiological disease

of paddy to iron toxicity. Agr. Res. Journ. of Kerala 1(1): 100-103.

Suthdhani, S. and S. Glasewiggram (not dated). Summary result of three

years (1962-1964) experiment on rice as affected by liming on acid

paddy soils. Report of Technical Division, Rice Department, Ministry

of Agriculture, Thailand.

Takahashi, J., C. Kanareugsa, P. Sawardee, P. Sonmuang, Y. Hasanthon,

H. Knunathai, J. Somhondumrongkul, 1979. Report on the study of paddy

soil fertility of Thailand. Department of Agriculture, Ministry of

Agriculture and Cooperatives, Government of Thailand and Japan Inter­

national Cooperations Agency.

74

Takigma, Y. and M. Kanaganayagan, 1970. Nutrient deficiency and physi­

ological disease of lowland rice in Ceylon. IV. Remedy for brozning

disease of rice. Soil. Sei. and Pit. Nutr. 16(1): 17-23.

Tanaka, A., R. Loe and S.A. Navasero, 1966. Some mechanisms involved in

the development of iron toxicity symptoms in the rice plant. Soil

Sei. and Plant Nutr. 12: 158-164.

Tanaka, A. and S.A. Navasero, 1966. Interaction between iron and manga­

nese in the rice plant. Soil Sei. and Plant Nutr. 12: 197-201.

Tanaka, A. and S.A. Navasero, 1966a. Aluminum toxicity of the rice

plant under water culture conditions. Soil Sei. and Plant Nutr. 12:

55-60.

Tanaka, A. and S.A. Navasero, 1966b. Growth of the rice plant on acid

sulphate soils. Soil Sei. and Plant Nutr. 12: 107-114.

Tanaka, A. and S.A. Navasero, 1967. Carbon dioxide and organic acids in

relation to the growth of rice. Soil Sei. and Plant Nutr. 13: 25-30.

Tanaka, A., R.P. Mulleriyawa and T. Yasu, 1968. Possibility of hydrogen

sulfide induced iron toxicity of the rice plant. Soil Sei. and Plant

Nutr. 14(1): 1-6.

Tanaka, A and S. Yoshida, 1970. Nutritional disorders of the rice plant

in Asia. Inst. Rice Research Inst. Tech. Bull. 10. 51 pp.

Tisdale, S.C. and W.L. Nelson, 1966. Soil fertility and fertilizers.

The MacMillan Company, New York, 694 pp.

Thawornwong, N. and A. van Diest, 1974. Influence of high acidity and

aluminium on the growth of lowland rice. Plant and Soil 41(1):

141-159.

Tomlinson, T.E., 1957. Changes in a sulfide-containing mangrove soil on

drying and their effect upon the suitability of the soil for the

growth of rice. Empire Journal of Exp. Agric. 25: 108-118.

Truog, E., 1948. Lime in relation to availability of plant nutrients

Soil Sei. 65: 1-7.

van Breemen, N. and L.J. Pons, 1978. Acid sulphate soils and Rice. In:

Soils and rice. IRRI, Los Banos, Laguna Philippines, pp. 739-761.

Vangnai, S., P. Attanandana and A. Taweteekul, 1974. Sulfide formation

and rice yield in Ongkharak soils (in Thai, English summary) Kasets-

art J. 8: 23-27.

75

Vlamis, J., 1953. Acid soil in fertility as related to soil-solution

and solid phase effects. Soil Sei. 75: 38-394.

Watson, K.K. and S.J. Lees, 1975. A procedure for the sampling and

testing of large soil cores. Proc. Soil Sei. Soc. Amer. 29: 589-590.

Watt, J.CD., 1969. Phosphate retention in acid sulphate pond weeds

from the Malacca area. Malaysia Agr. J. 47: 187-202.

Wright, K.E., 1937. Effects of phosphorus and lime in reducing aluminum

toxicity to aluminum toxicity. Plant Physiol. 12: 173-181.

Wright, K.E., 1943. Internal precipitation of phosphorus in relation

aluminium toxicity. Plant Physiol. 18: 708-712.

Yang, M.S., 1976. Effect of lime on characteristics of rice seedlings

in an acid sulphate soil (Korean, English Summary) J. Inst. Agr. Res.

Util (Korea) 8: 33-343.

Zashariah, P.K. and H.S. Sankarasubramoney, 1961. Pot culture studies

on salt tolerance of certain paddy varieties. Agr. Res. J. of Kerala.

1: 104-105.

Zuur, A.J., 1952. Drainage and reclamation of lakes and of the Zuider­

zee. Soil Sei. 74:75-89.

76

Appendix 2•1

Acid sulphate soil near Aparri, Philippines

USDA Soil Taxonomy: Sulphic Tropaquept. Profile Aparri, examined and

sampled 1 November 1979 by Le ngoc Sen and Robert Brinkman.

The site

Location near Aparri, Cagayan, Philippines. About 3 km SE of Aparri,

about 0.5 km E of small tidal creek. Map reference Philippines 1:50.000

scale, sheet 3375 III, Aparri, 18° 21' N, 121° 40' E.

About 1 m above mean sea level.

Landform and slope: young Holocene coastal plain, level.

Vegetation/land use: bunded wetland fields, grass fallow. Until a year

ago: open short grass and sedge swamp.

Climate: tropical monsoon climate; occasional typhoons; occasional

salt-water flooding.

General information on the soil

Parent material: Holocene marine alluvium

Drainage poor. Seasonally flooded to moderate depth. Moisture condi­

tions in the soil: upper few mm dry, moist to wet below. Ground water

at about 70 cm depth.

No surface stones or rock outcrops. No erosion except very locally

along tidal channels. Occasional salt-water flooding.

Human influence: field bunds and ploughing to 8 cm, started about

1 year ago.

Brief description of the profile

Deep, poorly drained, very dark grey silty clay with a greyish brown,

distinctly mottled subsoil and a wet, black to very dark grey, plastic

and sticky substratum. Structure is weak prismatic and blocky; the soil

is moderately porous throughout.

77

Profile description

Ap, 0-8 cm. Very dark grey (10YR3/1) moist silty clay; few fine dis­

tinct strong brown mottles; massive; dry hard, moist to wet plastic,

nonsticky; common fine tubes; many fine living and dead roots; clear

smooth boundary.

Al, 8-25/30 cm. Very dark grey (10YR3/1) moist silty clay; common fine

distinct brown (7.5YR4/4) mottles along root channels, many medium

distinct brown along prism faces in upper 5 cm, few in lower part;

moderate very coarse prismatic; moist to wet plastic, nonsticky; thin

continuous cutans on prism faces; common fine tubes and many fine

roots, both mainly vertical; clear wavy boundary.

Bg, 25/30-40/46 cm. Greyish bown (10YR5/2) moist silty clay; many

medium distinct light yellowish brown, brownish yellow and brown/dark

brown mottles; weak coarse prismatic and moderate coarse and medium

angular blocky; moist to wet plastic, nonsticky; thin patchy cutans on

all faces; common fine mainly vertical tubes; common fine living and

dead roots; clear wavy boundary.

Cgl, 40/46-60 cm. Black (10YR2/1) moist silty clay; only along ped

faces, common fine distinct dark reddish brown mottles with common fine

distinct brownish yellow mottles in upper part; moderate coarse pris­

matic and weak medium angular blocky; wet plastic, nonsticky; common

fine vertical tubes and roots; gradual smooth boundary.

Cg2, 60-90 cm. Very dark grey (10YR3/1) moist silty clay; common fine

faint dark brown mottles along root channels and few medium faint dark

reddish brown mottles along coarser pores; weak very coarse prismatic

and very weak medium angular blocky; wet plastic and sticky; common

fine mainly vertical tubes and roots; diffuse boundary.

CG, 90-110+ cm. Very dark greyish brown (10YR3/2) silty clay; many

medium distinct greyish brown mottles with indistinct limits; massive

and very weak angular blocky; wet plastic, very sticky; common fine

tubes and roots.

78

Acid sulphate soil in Sinacaban, Philippines

USDA soil taxonomy: Typic Sulfaquent. Profile Sinacaban was examined

and sampled on April 19, 1980 by Le ngoc Sen.

The site

The site is located in barrio Tidok, Sinacaban, Misamis occidental,

Philippines and is an uncultivated land with mangrove trees. This area

will turn into fishponds in the near future. Nearby the site, wetland

rice was cultivated and some fishponds were under operation.

Rainfall is ample in this place (>5.000 mm) and evenly distributed

throughout the year.

The site is influenced by diurnal tide. The difference between the high

and low tides is about 1 m. During the high tide the soil is submerged

to about 10-20 cm above the soil surface. During the low tide, ground

water is found at about 30 cm below the soil surface.

The topography of the site is flat. Many lobster mounds appears on the

soil surface (pH < 3) of this area.

In the newly constructed fishponds nearby, intensive jarositic mottles

were found on the dikes.

Profile description (from auger samples)

A : 0-10/15: color 10YR3/2, silty loam, non sticky. The dominant 1 2

mottles having color 2YR3/6, with the density of 10-20/dm partly

from dead mangrove leaves and from the eroded materials of the

adjacent mountains. There are fresh mangrove roots of 0.5-2 mm in

diameter and crab holes of 10 mm in diameter. Low organic matter.

A : 10/10-20/25 mm: color 10YR3/2. Less mottles than the upper layer.

No crab holes. Soil is relative stickier than the upper layer,

low organic matter.

A : 20/15-40: color 10YR4/1. Slightly sticky, high organic matter.

Clay loam. Root channels had a size of less than 1 mm in dia­

meter. Mottles color 2YR3/6.

C : 40-70: Very loose material high organic matter, color 10YR3/2.

C2: 70-100: The color of soils is 10YR3/2, very high organic matter.

Some fresh mangrove roots appear.

C_: >100: sandy material, gravel of >1 cm appear and big mangrove

roots are found.

79

THE EVAPORATION AND ACIDIFICATION PROCESS IN AN ACID

SULPHATE SOIL

Abstract

Fourteen undisturbed soil columns of 20 cm in diameter and 70 cm length

from an acid sulphate soil in Mijdrecht, Netherlands were used to study

the acidification process upon drying. Two groundwater levels: 40 cm

and 65 cm below the soil surface, 5 different durations of evaporation

and 2 agronomic practices were imposed.

Among treatments, averaged total acidity over 14 layers in the soil

profile did not show much variation as the cumulative evaporation in­

creased. The depth of the acidity maximum in the soil profile with low

groundwater varied with the presence or absence of peat on the surface.

Without peat, the total acidity maximum in the soil profile was about

35-40 cm below the surface, with a thin peat layer, they remained about

10 cm deeper.

The presence of peat layer on the surface reduced the rate of acidifi­

cation, presumably mainly by reducing evaporation rate and perhaps by

reducing the input of oxygen in the soil profile.

The average pH value over 14 layers along the soil profile was lowered

as the depth of groundwater increased from 40 to 65 cm. In treatments

with a low groundwater table, the average pH decreased sharply with in­

creasing evaporation: to about 3.5 after 140 mm of evaporation. The de­

crease was less drastic where groundwater remained high. Mulching or

plowing at the start of a dry season to reduce the flux of solutes by

capillary movement and maintaining the water table as high as possible

80

to reduce oxidation may be good management practices in acid sulphate

soils.

4.1 Introduction

The formation of acid sulphate soils results from the presence of sul­

fides , the introduction of aerobic conditions, and the lack of bases,

usually calcium carbonate, to neutralize the acidity. Soils may become

aerobic when they are drained for agriculture but also when there are

seasonal changes in soil drainage, e.g. by a lowering of the ground­

water table. Evaporation from bare soils may have the same effect owing

to the loss of soil water. Evaporation may also cause accumulation of

toxic salts in surface horizons because of upward capillary movement.

Low pH, high acidity and accumulation of toxins can degrade the pro­

ductivity of the soils. Results of field experiments about the effects

of changes in groundwater level on the acidity of acid sulphate soils

and on crop yields were reported by Beye (1973), Kanapathy (1973) and

Yin and Chin (1982), but basic information about the effect of evapo­

ration in the dry season is lacking. Field observations in Vietnam in­

dicate that plowing in the dry season followed by leaching of salts

accumulated just below the surface soil may depress the toxicity to

crops in acid sulphate soils (Vo tong Xuan, personal communication).

The objective of this study was to determine the effects of groundwater

levels and other factors related to the evaporation rate on the acidi-

ficiation process of an acid sulphate soil.

4.2 Materials and methods

An acid sulphate soil from Mijdrecht Polder in the Netherlands was used

for this study.

The soil profile consisted of a thin (10 cm) peat layer, somewhat com­

pacted, over 35 cm jarositic material, with a half ripe pyritic sub­

stratum. Before the experiment, the peat layer was removed except where

stated.

81

ci rculation heater 2000 W

40-

cm

65-

70

peat

•20 cm •

(in some columns)

— PVC pipe with bottom cover

jarosite clay

pyritic clay

groundwater table

wooden [ P

, quartz sand

"v -

PVC glue

latform I \ j glass wool| j

glass bottle of 0.7 liter

_̂ _ with scale i n mm of evaporation from soil surface

w alumi nium foi 1 — plastic funnel

— plastic tube

,̂ _ stand

Fig. 3.1 Cross-section of a soil column with low groundwater.

82

In spite of the artificial drainage in the polder the acid sulphate

soil has remained in its poorly drained condition, being protected by a

35 cm thick man-made soil cover. This was removed before sampling.

Undisturbed soil columns were collected in 14 PVC pipes with 20 cm in­

side diameter and 70 cm length (Fig. 3.1). One end of the PVC pipe was

sharpened in order to have a good cutting edge. The procedure used in

obtaining the columns was similar to that described by Le Ngoc Sen

(1982). The columns were excavated in two rows close to each other in

an area of 0.5 x 2 m (Fig. 3.2).

200 cm

50 cm

peat

Fig. 3.2 Place of soil columns in the original soil.

The filled PVC pipes were tied with rope, turned 45 degrees and dragged

up to the ground surface along the sloping side of the pit. The excess

soil material at the bottom was trimmed level with the cutting edge. A

PVC cover was placed over the top of the column, which was then in­

verted and kept wet during transport. In the laboratory, a 1.5 cm layer

of soil was removed from the bottom of the pipe, replaced by quartz

sand and connected with a plastic tube through a bored hole at the

side. The end of the plastic tube inside the pipe was covered with

glass wool and the other end connected with a source of water to regu­

late the groundwater table in the profile (Fig. 3.1). A PVC cover was

then sealed to the bottom of the pipe with PVC glue, the column repla­

ced in its original position and the top cover was removed.

Two of the fourteen columns were used as controls and were sampled at

the beginning of the experiment. The remaining ones were arranged at

random (Fig. 3.3).

83

groundwater table at 40 cm

14

© ® 10

7

® ©

5

7

© © 15

14

© ® 15

surface soi 1 di sturbed g.w.t. at 65 cm

14

© © 10

14

© @

5

groundwater table" at 65 cm

weeks evap.

directly sampled:

weeks evap.

Fig. 3.3 Arrangement of soil columns in the laboratory.

Two electrical circulation heaters of 2000 watts placed at 0.50 meter

above the surface of the columns increased the evaporation rate.

The depths of ground water were maintained at 40 and 65 cm below the

soil surface. Different combinations of treatments were imposed

(Table 3.1).

The high groundwater level, 40 cm below the surface was chosen to satu­

rate the pyritic horizons, which started at about that depth. The low

groundwater level, 65 cm, should allow some oxidation in the upper part

of the pyritic horizons.

At the end of a run, the bottom of each pipe was removed and the pipe

itself cut into two along the profile by electric saw. The columns were

then sectioned into 5 cm segments. In each segment, two samples of

25 ml were taken with the aid of a PVC auger of 5 cm diameter and

placed in plastic bottles, then mixed with 100 ml demineralized water,

shaken for one hour and centrifuged for 30 minutes at 3000 rpm. In the

supernatant liquid EC and pH were determined electrometrically. Total

acidity was determined by titration with 0.1 N NaOH to the end point by

phenolphtaleine as indicator. Total acidity comprises three kinds of + 3+ 2+

acid: H , Al and Fe . The former is neutralized directly during

titration, Al is hydrolyzed to A1(0H) releasing 3H+; and F e 2 + is

oxidized in the mechanically stirred solution during titration, pro­

ducing Fe(OH) and 2H . Vertical moisture distribution was determined

84

Table 3.1 Characteristics of different soil columns.

Column Groundwater Duration of Plowing Presence Presence

number level evaporation surface of peat of jarositic

(cm) (weeks) soil on surface crack

1

2

31'

4

5

6

7

8

9

10

11

12*

13

14

65

65

--

65

40

65

40

65

65

65

40

—

40

65

14

10

—

15

7

10

14

5

14

15

14

—

7

5

yes

no

no

no

no

no

no

no

yes

no

no

no

no

no

yes

yes

yes

yes

yes

no

no

no

no

no

no

no

yes

no

yes

no

yes

no

no

no

yes

no

no

no

no

no

no

no

1) control column

along all profiles except for the control columns 3 and 12. Bulked

samples over 10 cm depth increments were freeze-dried for sulphur

fractions and other chemical analyses, according to Begheijn (1980).

Samples of columns 4 and 10 were collected in 100 ml aluminium rings

for bulk density determination. In the extracts of columns 4, 10 and

11, determinations of Ca, Mg, Na, K, Fe, Cl, NO , SO, and HCO " were

made additionally. Except for HCO-, which was determined by carbon

analyzer after centrifugation, these determinations were made on solu­

tions stored in the refrigerator for 2 weeks after adding a few drops

concentrated HCl.

Some of the water samples from columns 4, 10 and 11 were also analyzed

for Ca, Fe, Mg by atomic spectrophotometer; Na and K by atomic emission

spectrometer; Al by spectrophotometer with pyrocatechol violet; Fe, Cl, 2-

NO» and SO, by ion-chromatography.

85

Freeze-dried samples of colums 3, 4, 10 and 12 were used to determine

CEC, Ca, Mg, AI and total acidity, and freeze-dried samples of columns

2, 3, 8, 12 and 10 for sulfur fractions.

3.3 Results and discussion

3.3.1 Evaporation

The evaporation rate appeared to be influenced by the level of the

groundwater table, by disturbance of the surface soil and by the pre­

sence of a peaty layer on the surface. The evaporation rate was about

Table 3.2 Evaporation rate, averaged soil moisture, EC, pH, total

acidity and basic cations of different soil columns.

Col umn

number

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1)

2)

Evaporation

rate

(mm/day)

0.82

0.66

0.00

0.73

1.47

1.37

1.69

1.28

0.99

1.19

1.61

0.00

2.14

1.54

Averaged value of

Not determined

Aver a

soil i

(mass

85

102

__2)

94

88

92

93

87

88

85

92

..2)

92

95

Sed1) Averaged

noisture EC

%)

7 layers in

(mS/cm)

0.93

1.02

0.79

1.11

1.03

1.16

0.97

1.28

1.60

1.89

1.11

0.82

0.97

1.06

Aver a

PH

3.95

3.97

3.78

3.96

4.19

3.77

3.90

4.04

3.70

3.61

3.93

4.25

4.15

4.16

the soil column

ged Averaged Averaged

total

acidity

(mol/m3)

1.71

2.07

1.04

2.50

2.12

3.01

1.78

3.44

11.84

16.96

4.56

1.74

1.77

2.16

basic

cations

(mol/m3)

11.5

12.8

9.2

14.0

12.9

14.4

12.0

16.2

13.8

14.0

11.9

10.0

12.2

13.3

86

1.5 to 2.1 mm per day with a high groundwater table and about 0.7 to

1.5 mm per day with a low groundwater table (Table 3.2). This amounts

to about 30-60 percent of the evaporation from a free water surface

measured in the experiment (3 mm/day). The presence of a peaty layer on

the surface decreased the evaporation rate by about 50 percent compared

with the columns without peat. Disturbance of the upper 10 cm decreased

the rate by about 20 percent.

3.3.2 Sulphur fractions

Four columns subjected to different durations of evaporation were se­

lected for sulphur fraction analysis. Total S, pyrite, jarosite and

water-soluble S are shown in Fig. 3.4. In general, total S and pyrite

of the four columns showed similar trends along the soil profile: both

total S and pyrite increased with depth. The difference in total S and

pyrite trends between the treated columns and a control (column 3) may

be attributed to the strong microvariability of the soil in the field.

The lower pyrite content in column 3 is related to oxidation along a

deep crack with a concentration of jarosite in this column; the low

average jarosite and water-soluble S contents must have been the result

of preferential leaching. Because of the variability between columns,

even taken adjacent to each other, no quantitative calculation was made

about the rate of oxidation and the results were studied by individual

columns.

3.3.3 The distribution of pH, total acidity, non-acid cations and

soil moisture in different soil columns

The distribution of pH, total acidity, non-acid cations and soil mois­

ture in water extracts of different soil solumns is presented in

Fig. 3.5.

pH: In general, the pH of the water extract of samples from all columns

showed the same trend along the soil profile (Fig. 3.5): a slight de­

crease in pH during the first 50 mm of evaporation only in the 40 cm

depth(cm) 87

u -l 0 »

20- iVi column 12

Q^pSa.,^^ 40- ,' ^ ^ T — — _ ^ _

60-• l \_\ a ^ci

low GUT

0 weeks

0 mm evap.

no peat

i • — i

* total S

o pyrite S

D water soluble 5

• j a r o s i t e

0 weeks, (w i th cracks) 0 mm evap. w i th peat

low GWT 5 weeks, 45 mm evap. no peat

2 3 mass f r a c t i o n S (%)

Fig. 3.4 Sulphur fractions of five soi l columns with low groundwater

table .

88

surface soil, followed by a drop of half a pH unit throughout the pro­

file as evaporation increased. For columns with a low groundwater level

the lowest pH values were observed at the pyrite-jarosite boundary at

35 to 40 cm; with high groundwater, about 5 cm higher (Table 3.3). This

difference is attributed to the upward movement of acidity from the

oxidation products of pyritic layers.

Table 3.3 Depths of total acidity maximum and pH minimum.

Column

number

1

2

4

Average

14

6

8

9

10

Average

13

7

5

11

Average

3

12

Average

Groundwater

table

low

low

low

low

low

low

low

low

low

low

high

high

high

high

high

control

control

control

Presence

of

+

+

+

+

-

-

-

-

-

-

+

-

+

-

+

+

-

+

peat

and -

and -

Total ac

maximum

45-50

40-45

45-50

45-50

40-45

40-45

35-40

35-40

30-35

35-40

45-50

50-55

40-45

30-35

40-45

55-60

45-50

50-55

Depths, cm

idity PH

minimum

35-40

35-40

40-45

35-40

25-30

40-45

35-40

35-40

30-35

35-40

25-30

30-35

25-30

35-40

30-35

30-35

25-30

30-35

89

•2 O

•M 20

40

60

20

40

60

20

40

60

0 weeks, 0 mm evap.

(with cracks)

with peat

-

-

-

-

\ 5 weeks, \ 45 mm \ evap.

\no peat

I I , <

" / f

' \ \

i i i • >.

10 weeks, 46 mm evap.

^>with \ peat

: >

• . . \ .

/,

i

v

i ix \

20

40

60

N. 1 5 weeks,

[ 125 mm 1 evap.

, y no C peat

i i i i

•f( \

i i i ' i

0 40 80120160 3 4 5 6 0.1 0.5 1 moi sture content vol%

5 10 50 1 2 5 .102040 PH , • . - ^ / -, , 3 , n o n - a c i d

t o t a l a c i d i t y (mo l /m ) c a t i o n s ( m o l / m 3 )

Fig. 3.5 The distribution of soil moisture content and pH, total

acidity, basic cations in water extracts of selected soil

columns with groundwater at 65 cm depth.

90

total acidity, maxima (mol/m ]

50

32

16

10

'î

O O low GWT

high GWT

• O

o

o o o

o—o

o o

• o

20 40 60 80 100%

Fig. 3.6 Frequency distribution of total acidity maxima of extracts

in the profiles.

91

3.3.4 Total acidity

The total acidity of water extracts along the soil profile shows a

clear picture with relatively small variations (Fig. 3.5).

Acidity maxima were found at 45-50 cm depth, just below the pyrite-

jarosite boundary, in columns with low groundwater and a peaty layer on

the surface; about 10 cm higher without peat (Table 3.4).

The positions of total acidity maxima for both high and low groundwater

treatments were higher in the profile compared with the control

(Table 3.4). As the evaporation increased, more acidity was developed

in the profile and the position of the total acidity maximum moved

upward.

Table 3.4 Averaged pH, EC, total acidity of the first 30 cm in the

profile of different columns.

Column

number

pH EC

mS/cm

Average

total acidity

mol/m3

1

2

3

4

5

6

7

8

9

10

11

12

13

14

4.05

3.90

3.92

4.00

3.59

3.49

3.54

3.51

3.31

3.10

3.37

3.64

3.79

3.62

0.95

1.05

0.76

1.15

1.24

1.16

1.08

1.36

1.50

1.98

1.26

0.64

1.14

1.08

0.75

0.89

0.38

0.99

1.27

1.19

1.13

1.77

5.57

13.88

2.94

0.79

0.83

1.04

92

The frequency distribution of the acidity maxima is shown in Fig. 3.6

for low and high groundwater levels separately. Although there are few

data points only, the peak concentrations of soluble acidity in the low

groundwater treatments (without peat) appear to be far higher than with

high groundwater. The total acidity of surface soil in treatments with

a thin layer of peat was less than without peat.

For both groundwater levels, the average soluble acidity over the whole

profile is about 3 mol/m3 (s = 0.3).

A comparison between the controls with a jarositic crack and without

cracks respectively shows that the subsoil in the column with a crack

has a lower pH, but less total dissolved acid than the column without

cracks; this may be ascribed to preferential movement of both oxygen

and leaching water into the subsoil along the crack under field condi­

tions before the experiment.

3.3.5 Basic cations

In general, the soluble basic cations did not show much variation be­

tween treatments at depths of 25 to 55 cm (Fig. 3.5). An increase in

soluble non-acid cations was found in surface soil only as the evapora­

tion increased. A sharp decrease in concentrations of non-acid cations

was found in soil horizons below 55 cm after 15 weeks (Fig. 3.5). Among

the control columns, the surface soil of the cracked core has a higher

concentration of basic cations; this is probably due to less leaching

water passing through the surface soil near a crack than further away

(short circuiting).

3.3.6 Soil moisture

As expected, the soil moisture contents of different layers along the

profile increased with depth. In the half ripe subsoil the gravimetric

soil moisture content of the lower layers exceeded 100 percent. The

moisture distribution showed little variation among treatments. Dis­

turbance of the surface layer allowed this layer to dry out (Fig. 3.5),

93

but did not appreciably change the soil moisture distribution along the

profile. The disturbed layer may not have been thick enough to decrease

drastically the evaporation from lower horizons.

3.3.7 Changes of pH and total acidity of water extracts with

cumulative evaporation

Average pH and total acidity over the profile

As the evaporation increased, the average pH of water extracts along

the profile decreased (Fig. 3.7). In columns with a high groundwater

table, the pH decreased slowly with increasing cumulative evaporation.

It decreased sharply in columns with low groundwater. About 140 mm of

evaporation in low groundwater treatments resulted in an average pH

about 3.5. Except in three columns (9, 10 and 11), the average total

acidity of water extracts over the profile did not show much variation

with time (Fig. 3.8).

•v 4.4

<u 4.2 -

4.0

o> 3.8

3.6 -

3.4 60 100 140 180

cumulative evaporation (mm)

Fig. 3.7 Average pH of extract over the profile in relation to

cumulative evaporation.

94

~ 20 en •5 15

rU O

O a .

10 -

5

3

2 s - s -QJ O» > > fö O

0.5

-

r

--

\

A

O

•

1

c o n t r o l

low GWT

h i g h GWT

O O

o- -o

l l 1

C \

\

0

•

i

A \

\

i

\ \

^

•

i 0 20 60 100 140 180

cumulative evaporation (mm)

Fig. 3.8 Average total acidity of extract over the profile in relation

to cumulative evaporation.

Average pH and total acidity of water extracts in the upper 30 cm

Regardless of groundwater table levels, the average total acidity over

the upper 30 cm did not show much variation (Fig. 3.10, Table 3.4). Average

pH of surface soil for both groundwater treatments remained 3.5 until

the cumulative evaporation exceeded about 100 mm (Fig. 3.9). After that,

the pH tended to fall slightly below 3.5.

•r- 4.5

•°A

• u 3.5

« XL

£ ** 3.

CD

A control

O low GWT

• high GWT

20 60 100 140 180 cumulative evaporation (mm)

Fig. 3.9 Average pH of extracts over the 30 cm of surface soil in

relation to cumulative evaporation.

95

15

10

5

3

2

1 I

0.5

I 0.3

0.2

i

!k

1

O

6

1

o

1

•

o o

1

°®

9D

•©

o • •

A control

O low GWT

• high GWT

i i l 1

0 20 60 100 140 180 cumulative evaporation (mm)

Fig. 3.10 Average total acidity of extracts over the 30 cm of surface

soil in relation to cumulative evaporation.

3.3.8 General results and discussion

Average total soluble acidity over the soil profile did not show much

variation with cumulative evaporation or with differences in ground­

water levels or other factors related to the evaporation rate.

The position and magnitude of the soluble acidity maximum in the soil

profile depends on the groundwater table and the presence of peat. A

groundwater table below the top of the pyritic layer apparently created

conditions enhancing the oxidation of pyritic materials, resulting in

high acidity maxima.

Hydrogen ions would be expected to move faster in the soil than Al (or

Fe) ions because the diffusion coefficient of hydrogen ion is about

three times higher than of Al and Fe.

96

Changes of average pH over the soil profile with cumulative evapora­

tion depended on groundwater depth. In high groundwater table treat­

ments , pH gradually decreased with cumulative evaporation whereas it

decreased sharply where groundwater table was low. The pH of the sur­

face soil only started to drop after about 100 mm of evaporation, in

both groundwater levels.

The average pH turned out to be a more sensitive indicator for the

development of acidity during the 15-week period of evaporation than

the average soluble acid concentration.

With longer periods and higher totals of evaporation, as would occur

during the dry season in monsoon climates, pH is expected to become

less diagnostic; average soluble acid over the profile and in the sur­

face horizon should then become better indicators for the potential

growth of crop plants.

Further research is needed to ascertain the critical amount of evapo­

ration causing unacceptable acidification with different groundwater

levels and different depths to pyritic material in the field under dif­

ferent agronomic practices.

Disturbance of 10 cm surface soil only lowered the evaporation rate by

about 20 percent. Mulching at the start of the dry season would seem to

be a promising management practice in acid sulphate soil, even through

its effects in this experiment were small. Further work along this line

is needed.

The presence of a peaty layer on the surface reduced the evaporation

rate and the total soluble acidity in the soil profile. The peaty layer

was relatively dense and slightly platy, however. After ploughing it

would have been broken up and incorporated in the Ap horizon.

Because of the local variability of acid sulphate soils, only gross

differences become apparent by traditional small-sample methods.

The variability, as shown by the data in this study, consists of two

parts: a limited variation about a mean, and some outliers indicating

extremely acid, toxic or potentially toxic conditions. Therefore, sam­

pling methods based on bulking even large numbers of subsamples do not

fairly represent conditions in most of the soil mass.

97

Sampling methods should either be based on extensive replication, or

depend on close observation and recording of soil differences over

small distances, with interpretation of individual results in relation

to the observed characteristics of each sample or profile. In both

cases, efforts should be made to estimate the frequency distribution of

the different values encountered.

The present experiment represents about one month of unchecked evapo­

ration from soils with shallow groundwater during the dry season of a

monsoon climate. Therefore, it only shows the beginning of the acidi­

fication that bedevils rainfed wetland crop production on acid sulphate

soils in such climates.

It is clear, however, that even at relatively low evaporation rates, a

groundwater table below the top of the pyritlc layer is far more

dangerous than a high groundwater table, although this tends to accel­

erate evaporation and transport of existing acidity to the surface

horizon.

Minimizing evaporation during the dry season appears to be the next

most important management measure if acidification is to be minimized.

Acknowledgement

The author wishes to thank Prof. L.J. Pons and Mrs. N. Pons for their

interest in the study, Dr. N. van Breemen, Dr. R. Brinkman and Prof.

L.J. Pons for their valuable suggestions and comments, Mr. L.Th. Be-

gheijn, Ms. Els Feenstra for her major contribution to this study and

the soil laboratory staff for their help in the chemical analysis.

3.4 References

Begheijn, L.Th., 1980. Methods of chemical analyses for soil and water.

Department of soil science of geology, Wageningen Agricultural Uni­

versity, Wageningen, The Netherlands.

98

Beye, G., 1973. Acidification of mangrove soils after empoldering in

Lower Casamance. Effects of the type of reclamation system used. In:

H. Dost (ed). Acid sulphate soils. Proceedings of the International

symposium 13-20 August 1972, Wageningen. ILRI Publ. 18, vol II:

359-372.

Kanapathy, K. , 1973. Reclamation and improvement of acid sulphate soil

in West Malaysia. In: H. Dost (ed). Acid sulphate soils. Proceedings

of the International Symposium 13-20 August 1972 Wageningen. ILRI

Publ. 18, Vol II: 383-390.

Le Ngoc Sen, 1982. A simple, low-cost method to collect undisturbed

cores of acid sulphate soil profiles for the study of water and

solute movement during reclamation and use for wetland rice. In:

H. Dost and N. van Breemen (ed). Proceedings of the Bangkok symposium

on Acid sulphate soils. ILRI Publ. 31: 381-388.

Yin, T.P. and P.Y. Chin, 1982. Effect of water management on perfor­

mance of oil palms on acid sulphate soils in Peninsular Malaysia. In:

H. Dost and N. van Breemen (ed). Proceedings of the Bangkok symposium

on Acid sulphate soils. ILRI Publ. 31: 260-271.

99

EFFECTS OF ACID SULPHATE FLOODWATER ON THE GROWTH OF RICE

AND ON THE CHEMICAL CHANGES IN THREE ACID SULPHATE SOILS

Abstract

The one-time and cumulative effects of acid sulphate floodwater on the

growth of rice and on the chemical changes in three acid sulphate soils

were investigated in two successive pot experiments. The pH of acid

sulphate floodwater was varied from 3.5 to 5.9, aluminium concentration

from 0 to 300 mg/1 and iron from 0 to 500 mg/1. These values are repre­

sentative for floodwater draining from acid sulphate areas in Vietnam.

Pots contained 3.5 kg soil and were planted with 2 seedlings of 21-day-

old IR36. The experiments were replicated 3 times.

The responses of three acid sulphate soils to added acid sulphate

floodwater were different in magnitude but similar in direction of

change of various chemical parameters. pH in acid sulphate floodwater

alone did not affect the chemical changes of three acid sulphate soils; 3+ 2+

whereas the presence of Al and Fe in acid sulphate floodwater pro­duced low pH and enhanced the solubility of Fe.

The pH of acid sulphate floodwater alone as low as 3.5 showed no effect

on the growth of rice at early stage. Dry matter yields were negatively 2+ 3+ 3+ 2+

correlated with the applied Fe and Al . High Al and Fe concen-3+

trations in acid sulphate floodwater increased the Al and N contents

in plants and decreased their Mn content.

100

Total acid input from the floodwater per unit area was estimated from 3+ 2+

amount applied, Al and Fe concentrations and pH. This variable was

negatively correlated with dry matter yield and could be used to pre­

dict the yield reduction due to acid sulphate floodwater provided that

the chemical composition of soil solutions did not reach limiting tox­

icity levels.

4.1 Introduction

During the rainy season, floodwater in the Mekong Delta flows gently.

As it passes over acid sulphate soils, the water collects considerable

amounts of acid and other chemicals. The floodwater is fairly acid at

the beginning of the rainy season, becomes more acid with time and then

becomes nearly neutral. When the acid floodwater flows over the slight­

ly acid sulphate and normal soils of nearby areas it causes poor rice

yields and changes soil properties. And when the acid floodwater

reaches the river through surface runoff it pollutes the river water.

Farmers in some areas use this polluted water to irrigate their field

during some parts of the cropping season.

The chemical properties of acid sulphate water vary from place to place

(Table 4.1). Its acidity is due to the presence of aluminium and ferric

sulphate and sometimes of free sulfuric acid. High aluminium and iron

concentrations in water may adversely affect rice plants. Rice was not

affected at pH as low as 3.5 in the culture solution at the vegetative

stage (Tharwornwong and van Diest, 1974) but suffered from toxicities

at 25 to 40 ppm of water soluble aluminium (Cate and Sukhai, 1964;

IRRI, 1964) and at about 500 ppm of water soluble iron (Ponnamperuma,

1955).

The objectives of this paper are: a) to study the effects of acid sul­

phate floodwater on the chemical changes of three acid sulphate soils,

and b) to determine whether the acid sulphate water has adverse effects

on rice.

101

Table 4.1 Composition of acid sulphate water at various locations in

Vietnam «/

Site

Groundwater at Haiphong expt. station

Binh lue, Nam ha

Kinh Thang

Vam Co Tay River

Groundwater Vam Co Tay

Stagnant water in some ponds

Few places (not specified)

PH

4.6-7.0

5.9

2.4

3.9-7.0

2.0

2.5-3.0

2

SO4"

400-1800

320

13000

-

-

2000

-

Content mg/

Cl"

400-1800

- b/

1110

-

-

-

-

1

Al3 +

0-0.58

-

-

-

0-456

500-800

1000-1500

Fe2+

0-543

-

-

-

0-453

-

-

a/ Le van Can; personal communication. Such waters are used for irri­

gation of rice if their pH exceeds 3.5 when fresh water is not

available.

b/ not determined.

Table 4.2 Chemical properties of three acid sulphate soils.

Soil type

pH (1.1)

EC

%C(%)

N(%)

CEC

Active Fe(%)

Mn(%)

Available P (ppm)

Sinacaban

3.95

39.5

5.86

0.31

14.90

5.3

126.0

5

Leganes (Iloilo) Aparri

3.90

8.49

1.55

0.11

30.9

3.0

0.001

2

3.93

19.1

4.46

0.34

36.80

4.02

179.0

1

102

4.2 Materials and methods

Three acid sulphate soils from the Phillippines were used. Their chem­

ical properties are listed in Table 4.2. Four-liter pots, with glass

tubes at the bottom for drawing out the soil solution, were filled with

3.5 kg air dried soil. The soils were leached with demineralized water

to bring the EC of the soil solution to less than 1 mS/cm. Fifty mg/kg

of N, P and K were incorporated in the upper few cm. Different kinds of

acid sulphate floodwater, depending on the treatments, were applied on

wet soils and recycled 5 times to move of the fertilizer down in the

soil. The different compositions of acid sulphate floodwater are listed

in Table 4.3. These were made with AI2SO4 or NaOH. Twenty-one-day-old

IR36 seedlings were transplanted. Soil solutions were collected in test

tubes previously flushed with nitrogen gas, before and just after

transplanting, then once a week for 5 weeks and biweekly thereafter.

The solutions were analyzed

8 weeks after transplanting.

3+ 2+ 2+ 2+ + The solutions were analyzed for AI , Fe , Ca , Mg and K up to

The pH of surface water and soil solutions was measured directly by pH

meter. The soil solutions were acidified with a few drops of 6 N HCl to 2+ 2+

prevent oxidation of Fe and Mn . Subsequent analyses of the acidi-3+ 2+ 2+ 2+ +

fied solutions were made. AI , Fe , Ca , Mg , K and Na were deter­mined directly by atomic absorption spectrophotometer.

3+ 2+

Plants observations every week monitored Al and Fe toxicity symp­

toms. Plant heights were measured weekly. Eight weeks after trans­

planting the plants were cut and their dry matter weights recorded.

Plant samples were dried at 80°C for 48 hours, ground, stored in poly­

ethylene bags, and redried before analysis. Nitrogen was determined by

wet digestion with H2SO4 according to the micro-Kieldahl method

(Yoshida and others, 1976). P was determined colorimetrically by the

vanadomolybdo-phosphoric acid yellow-method after dry ashing 4 hours at

490°C (Yoshida, 1976); Mn 2 + , Na+, K+, Ca 2 + , Mg 2 + , Fe 2 + , and A l 3 + were

determined by atomic absorption spectrophotometry after digestion in

ternary acid mixture (HNO3, H 2 S0 4 and HC104).

103

Table 4.3 Compositions of acid sulphate floodwater (ASFW) in the

different treatments.

Treatment

no. pH

Content mg/1

Al 3+ Fe 2+

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 a/

3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 4.4 4.4 4.4 4.4 4.4 4.4 5.0 5.0 5.0 5.0 3.5

0 50

100 300

0 50

100 300 100

0 50

0 50 0

50 0 0 0

50 0

0 0 0 0

100 100 100 100 500

0 0

100 100 500 500

0 100 500 500

0

a/ Demineralized water was used

4.3

4.3.1

4.3.1.1

Results and discussion

Effect of acid sulphate floodwater on the chemical changes

of acid sulphate soils during the early growth period of

rice

Effect of pH of floodwater

The influence of acid sulphate floodwater on the chemical properties of

acid sulphate soils varied from soil to soil and season to season

(Figs. 4.1-4.9). None of the soils showed any marked difference in the

chemical properties of their soil solutions by varying only the pH of

the floodwater (Figs. 4.1-4.3). Low pH in association with high alu­

minium and iron concentrations in acid sulphate floodwater resulted in

104

pH i soil solution Flrst Cr°P

11 pH of ASFW *\ ' 3.5 o 5.0

5 _\v «3.8 H5.9 ILOILO \ D4.4

4

1 I ^ I ^ I I ^ ^

Second Crop

^ ^ ^ F f 6 7 1 2

Week Number

Fig. 4.1 Effect of pH over aluminium and iron in acid sulphate flood

water on the changes of pH in the soil solutions of three

acid sulphate soils for two cropping seasons; IKRI, 1981.

105

!

i

<u 60

cl

ja 01

X I 4-1

d o 1-1 <u 4-> <0

» O O

(0

o .

d

ao d

•H O. o. o l-l u o s

01 4-1 co

-C Cu

1-4 d w

j d

14-1 O

Cl o 14

•H

•O d

i-i 01 > o » o<

CM

4J Cl

01 X I

CO CO l-l ON 4-> rH a dj U I-H d 06 o S U M

00 •H f *

106 Fe in soil Solution mg / I 1500

1000

First Crop

500

100 -

Second Crop

—

-

I—H

pH of ASFW 7 3.5 • 3.8 • 4.4 O 5.0 • 5.9

ILOILO yT

^ \ _^_»-^*<ti-^"

2500

2000

1 5 0 0 -

1000 -

5 6 1 2 3 4 5 6 7 8

Week Number

Fig. 4.3 Effect of pH over aluminium and iron in acid sulphate flood

water on the changes of iron concentrations in the soil

solutions of three acid sulphate soils for two cropping

seasons; IRRI, 1981.

107

a lower pH and higher concentrations of iron in the soil solutions

(Figs. 4.1-4.3).

The decreasing concentrations of iron in the soil solutions for Aparri

and Sinacaban and the increasing concentration in the soil solution for

Iloilo soils during the second crop indicated the difference in the

chemical properties of three soils (Figs. 4.1-4.3). Both seasons, low

pH in acid sulphate floodwater produced low pH in the soil solutions of

all three soils (Fig. 4.1). The higher values of pH starting from

transplanting of the second crop were because the soils experienced a

month of water-saturated fallow, in which demineralized water was added

a few times to compensate for evaporation loss when pots were not

closed tightly with a plastic cover. The increase of iron concentra­

tions in soil solutions during the early growth period of rice on Sina­

caban and later in Iloilo acid sulphate soils was due to increasing Fe

solubility by chemical reduction (Ponnamperuma, 1955).

3+ Regardless of pH and seasons, Al concentration in the soil solution

showed no variation (Fig. 4.2) because of the high adsorption capac-3+

ities of soils and the uptake of Al by the rice plant.

4.3.1.2 Effects of iron concentration in acid sulphate floodwater

During the first crop, acid sulphate floodwater produced a) a decrease

in pH levels (Fig. 4.4), b) no marked effect on the concentration of 3+

Al in Aparri and Sinacaban soils and a slight increase in the concen-3+

tration of Al in Iloilo soil (Fig. 4.5), and c) an increase in con-2+

centration of Fe with time (Fig. 4.6) irrespective of Fe levels.

Throughout the period of observations, high concentration of Fe in the

acid sulphate floodwater produced low pH in the soil solution

(Fig. 4.4), irrespective of soils. The concentration of iron in the

soil solutions varied from soil to soil (Fig. 4.5). Sinacaban soil had

a markedly high concentration of iron in the soil solution, which was 2+

toxic to rice plants, whereas Fe concentrations in Aparri and Iloilo

did not reach a toxic level at transplanting time of the first crop.

110

AI in soil solution mg/ l

First Crop Second Crop

SINACABAN

f^lt^^i^^

Week Number

Fig. 4.6 Effect of iron over pH and aluminium in acid sulphate flood

water on the changes of aluminium concentrations in the soil

solution of three acid sulphate soils for two cropping sea­

sons; IRRI, 1981.

Ill

Iron in acid sulphate floodwater contributed to the high acidity in the

soil by the oxidation of FeS04 and the subsequent release of H2SO4 into

the soil solution.

During the second crop, the trend in the chemical composition of the

soil solutions differed from the first crop. The pH of Iloilo soil

gradually increased with time, while there was a slight decrease in pH

2 weeks after transplanting in the Sinacaban and Aparri soils, respec­

tively (Fig. 4.4). The Aparri and Sinacaban soils had a slight increase 2+

in the concentration of Fe , whereas the Iloilo soil showed a gradual 2+ 3+

increase in Fe concentration (Fig. 4.5). A little variation in Al

in the soil solutions was observed in Aparri and Sinacaban soils

(Fig. 4.6) regardless of iron concentrations in acid sulphate flood-

water.

2+ Both seasons, the higher concentration of Fe in the acid sulphate

floodwater produced lower pH and enhanced the release of iron in the

soil solution.

2+

The decrease in pH and increase in Fe concentrations in the soil so­

lutions of the Iloilo soil may have been due to the strong chemical re­

duction process, which dominated the reactions of acid sulphate flood-

water.

4.3.1.3 Effects of Aluminium

3+ The influence of Al in acid sulphate floodwater on the chemical

2+ changes of three acid sulphate soils showed the same trend as of Fe

3+ for the first and second crops (Figs. 4.7-4.9). As the levels of Al

in acid sulphate floodwater increased, the pH of the soil solutions 2+

decreased, the concentrations of Fe increased (Figs. 4.7-4.9) and the 3+

concentrations of Al did not change.

2+ The higher concentration of Fe in the soil solution was due to the

increasing solubility at low pH (Ponnamperuma, 1955). The general con-

112

PH in soil solution First Crop Second Crop

7 1

Week Number

Fig. 4.7 Effect of aluminium over pH and iron in acid sulphate flood

water on the changes of pH in the soil solutions of three

acid sulphate soils for two cropping seasons; IRRI, 1981.

113

AI in soil solution

mg/l First Crop Second Crop

^====—T^~^i^~^i

Week Number

Fig. 4.8 Effect of aluminium over pH and iron in acid sulphate flood

water on the changes of aluminium concentration in the soil

solutions of three acid sulphate soils for two cropping

seasons; IRRI, 1981.

Fe in »o» solution mg/l 1500

114 First Crop Second Crop

500

150

-AI of ASFW(mg/l>

0 0 ' " « A D50 • 100 • 300 )

-

i i l

100-

2500 -

2000-

1500

1000

500] rf ' i i i

6 7 1 2

Week Number

Fig. 4.9 Effect of aluminium over pH and iron in acid sulphate flood

water on the changes of iron concentrations in the soil

solutions of three acid sulphate soils for two cropping

seasons; IRRI, 1981.

115

3+ stancy of Al concentrations in the soil solution was presumable due

to the buffering capacity of the soil system.

4.3.2 Effects of acid sulphate floodwater on plant dry matter

yield and chemical compositions of IR36 on three acid

sulphate soils for two seasons

4.3.2.1 First crop

Eight weeks after transplanting, the plants were harvested, dried and

weighted. Dry matter (DM) yields are presented in Table 4.4. Low pH and

high iron concentration in the soil solution of Sinacaban acid sulphate

soil (Fig. 4.10) resulted in the poorest DM yield among the three soils

(Table 4 ) . Rice suffered severe iron toxicity one week after transplan­

ting for all treatments of Sinacaban soil and there was no significant

difference in DM yield.

A distinct trend in plant DM yield was observed in Aparri and Iloilo

acid sulphate soils (Table 4.4). Lower pH (3.8) in association with 3+ 2+

high Al and Fe concentrations in acid sulphate floodwater caused a 3+

decrease in yield. The greater effect of Al on plant DM is seen in

Fig. 4.10. DM yield decreased sharply as the concentrations of Al in 2+

acid sulphate water increased. In contrast, Fe concentrations in acid

sulphate floodwater up to 100 mg/1 did not influence DM yield. The ef-2+

feet of Fe on DM yield showed little variation.

The chemical composition of IR36 at 8 weeks after transplanting under 3+ 2+

the influence of pH, Al , and Fe of acid sulphate floodwater is

presented in Table 4.5. The content in plants was slightly affected by

changes in pH of the acid sulphate floodwater applied. At low pH,

plants tend to absorb more N in the form of ammonium, and less metallic 3+

cations (Table 4.5). The concentrations of N and Al in plants in­creased as levels of Al in the solution increased whereas the Mn con-

3+ tent showed the reverse (Table 4.5). The high concentrations of Al

t 2+

3+ in plants as levels of Al in acid floodwater increased may be due to

the high absorption capacities of plants. The concentration of P, Fe

116

Plant dry matter yield ( g/pat )

First Crap

500 (mg/1)

Fig. 4.10 Effect of pH, aluminium and iron in acid sulphate flood

water on plant dry matter yield of IR36 in three acid

sulphate soils for two cropping seasons; IRRI, 1981.

117

v O CO

os

o

l-H tl

•H

>> H Ol

•a 4-> d

oi x l +J •

l-H

u 1-1

o „ 9 M

Ö o (A

oi

2 » •d 9< oo * 'H 10

o m 3 o *»

d K

l - s sa 8 « S* s 3

S "H

« • O QJ

U 4J H o xi D 4J

«M <4H d W O

0 1 rH

a H

31

O

a o

o a.

ai •H !»

<u 4-1

d eo

XI co u

d a oi 2

U u CO

d a

x i

01 PH

•M d oc « a

H

4-1 10 4J u d u oi H a

m MH MH MH ai

u u X X X X CQ ï O CO

r ^ o o « - i r - i f o c n o o i o « - ' v O r - « o c o i o r ^ . N 3 ' r * » o O ' * ï - * 3 , i - < H s ï \ û o » J O c o H o r o e O f l O > * H O ^ f l O H O N O

r H O O O C O O O O O v O r ^ r H O O O v O ^ " O O O r H

'M 01

T3 U

MH MH MH MH Ol

•o U

X co

u X co

MH 0)

•o

•o o u

X X I X X co co a) co

X X X X CO ( 0 CO CO

o o - * i ^ o

vo CO CO 00 »o co CM »» o >J3 • ï c o o o i i-H CM O m a n

oo uo r - oo

TJ TJ TJ u

T3 T l T l CJ U

X

0 O C M U 0 H H C O i-l rH IT) i-H i-i r~ I H o o c o o co > * o

•o u

00 CM

X

co

dj 01 Ol 01 Ol

u u o o u X X I X X X X X X X X i X

coco CO c o c o c o c Q c O co

c M o o i - H C O v o c s i r ^ m ^ v o c M c o i - i i r i ^ t v o r ^ T - i o o r ^ c x t o o u o ^ " 0 > T H < M f - i o o \ û r ^ m i n r H o % c o ^ " » - H r ^ o > o ^ i o

c M > - i o r ~ - ' - ( o \ v o o o v o c M o o > o > o e o r H c M o o o r ^ o CM CM rH rH

01 •o -o

X X co

C\ CM rH co «* o\

01 T l

u o X X CO 10

i-t m i n \o o\ vo

MH 01

en CM

CM CM i - l i - l CM

M-l 01

X co

CM CM

u X CO

vO

o

X X CO CO

o i o f - ~ * 11 co r » CM

• * O v O CM CM i-i

X X X

vO M3 I— « * « * CM

i n CM r » CM CM rH

X X X co co

•* m m

CM CM

o

X CO

i n o

CM co co m i-i CM CM i-i

o

Ol

M3 CM

CO 00

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o H H H i / i i - i i - i i n i n H i/i t o

o o o o o o o o o o o o o o o o o o o o o i n o o m o o o m i n m

rH CO i-l CO i-l

o o o o o o o o o o o o o o o o o o * * - t f " » ~ t f ~ » * * o o o o i n o " i

c o c o c o c o c o c o c o c o c o « * « * > * - * » * ~ * i n m i n i n c o i n

i H c M c o - * i n v o r ~ . o o a i O r - i c M c o » * i n v o r ~ o o c j \ 0 ' - i r - l i - l r - l r - l i - l r - I r l i - l r - l r - I C M C M

4-1 a CO u

d 00

o d 0 1 u co

u 0 1

4-1

0 1

a co m 01

X I 4J

X I 4J

O 4-1 0 10

01 0 1 4-> E CO 0 1 n oo

d 01 co

j a u 4-1

01 d PH

•H O. •H

T3 4J rH r^ 01 3

^ d U co 01 u

S3 CO O . S • .

CO rH rH 01 Ol >

01

•o * « m «

d 4J CO co 01 a d O 01 S rt 4-1 01

MH >>MH

col

118

%

io u

•H

a .0 u .

t-H OJ 0 0

M ON

o 3 u 01 4-1 ra

•a o o

0> I1"1

4J -H

r1 n m m

•H 4J u a 10 j j

a< o d

n

+ CM

0>

c «

f'

" 10

%< a a

«H O

M +J u gj vo

CO <H « M M

ai rH £> <0

H

1 ai

<

PH

a

s

00 s*

10 S* iz; «->

« s*

/ - s CM 5*

a s«

a 01 p .

rH P<

a ri *

10 3-8

« **

PH a *

» S*

O Ol

« PH

st m vo o \ * J m CM «* CM m

ci os m I N m

m CM C\ 00 CM vo oo co n co

m m «er -tf vo

rH rH rH rH rH

O O O O O

m r» oo r» oo

r~* r-* r-t r* rH

O O O O O

r - CM co oo co rH CM CM CM rH O O O O O CO CO

co

in CM O

m

vO

co

VO CM

O

VO CM

O vO

co

VC CM

O

CM O

t-H vO

co

vo CM

O

rH

CM co co

CM

O

CM co

rH CM CM CM rH

CO Ol O O « * 1 ^ « * CM CM CM CO CO

sO N N vO ON CO CO o

oo - * r - co CO « * CM co

vo vo oo o rH rH rH CM

rH rH rH CM CM CM CM CM

O O O O

VO (M vOvO s f • * - * «

O O O O

OO vo CO vo O rH rH O

co co co co

O M » 00 H rH rH rH CM

O O O O 00 rH 00 00 O CM O vo

CM CM CM rH

m oo « * o cv

co co - * m m

01 > <-> 0) rH

rH — 60

zi e

o vo CO 00 -f m H

r^ O r^ rH CM m 00 00 i-t r* r* rH

O in rH ON

vo r- o st CO H

in «3- r-o CM r» i-H rH CM

m vc in m vo -tf

o o o o

r ~ . r - . o v r -

l-H l-H 1^ rH

O O O O

oo m co «tf r H CM CO NJ -

m in O ON in * * r— ON

co co co co

vo in vo ON CM CM CM CM

O O O O

CM -tf vo O r— o vo co

i-H CM CM CO

CM - * i n i n 00 rH CO CM rH

o CM m co -» ~*

rH rH CM CM CM CM

~ t CO O - * «a* m

r» • * CM O rH rH

CO CO CO

ON 00 ON

in m -tf oo o ON

o o o o m o o

01 > - - N

01 rH

OO

<u a |JH ^

O O O

r» r— ON

ON CM O H ( V | s f

N - * 0 m -tf ON

• J m o CM CM CO

oo o oo M f J O

vo - * CM oo - * m CM CO

vO vo vo 0 0 ON ON

r» vo vo co co co

o o o o o r^ in

o o

CM CM CM CM

O O

m co

-» -tf • t

o o

co m rH o

co co

ON ON r-i t-H

• » O o

-» m 00 ON

* • I-H rH

O

oo rH

O

oo

-tf • o

m I-H

CO

r— rH

• o

i~-r~-

CM

4-> d 01

a 4-1 10 01 u •u

+• CM 01 N •o d 10

+ co rH

< u 01

> o

•0 V 00 10 u 01

> <

Ul 4-1 d 01

a 4-> M 11 u 4-1

+ CM 0> (•H

•o d 10

« OH

u 01

> 0

•o 01 00 10 u 0)

> <

co 4-> d 01

a 4J 10 01 u 4-1

+ co rH

< " 3 d a

M •4

u Ol

> 0

•o 01 00 10 V4 Ol

> < XII u |

119

4H O

O u

a J3

Ö W 0 § H M

O) ,

s & | ö "•§

(4-1 d

u

10

O« to

W o ca

•o •rl t ;

at 2

° S co

u| -o + -H CM O

t l 10 N

O

•o ""j S o

A i g

co

. 10

-» S" 101 <

P i d

•H

' M 4 j

4-> Oi U U vo

>*M CO * M Bi

VO

t l r-l i O

« H

E <U P i

< P .

(0 S« CJ v_/

S3 w

<0 ï « la ^

r-\ OM 3 «

^̂

^̂

B 1) P i

rH P i

S i-J Pi < P i

0 0 » « 2 w

co H

/ — i OM S «

s - r

S5 **

P,

CO CM CM CM 1 /1

m co in <r oi CM ~* co co * *

oo oo co I-M oo l-M ~ * CM I-M

CM CM CM CM - * i - l r H i-M i-M r M

O O O O O

00 OV 00 00 00 l-M r M i-M i-M r M

O O O O O

CM Cv I -M i-M C M

- j i n i n m n

o o o o o

O CM i n CM co M n i / i t ^ t ^

CM

en CM

O

1-M

CM

O l CM

O

O o o

CM

CM

o

vO

CM

l-M CO

o

CO

CM

00 CM

O

CM vO

i-M CM CM CM i - l

~* 00 O VO r*. co o i o i r i CM r H

m •» o co va N r^ vo

CM r M CM O l CM i-M i-M

oo vo co * * i-M i H i-M i-M

O O O O

rM CM i-M t-M CM CM CM CM

O O O O

vu O u"> !/"> m vo vo m o o o o

vo oo r» CM oi oo vo r̂

co • * • * vo CM CM CM CM

O O O O

r^ CM r» co C O CO CM CM

in oo >* o en

co co >* 1/1 t/1

o - * co CM

co o O vo - * co

o

CV l-M

O

co

o

o

CM

O co

o

o

o

l-M

O

VO

O

l / l CO

CM

VO CM

O

vo

00 OM l-M

VO vO

CM l-M

VO t-M

O

CM CM

O

CO VO

O

r -

l-M

m CM

o

m CM

vO co CM Ol CM

O Ol r-~ vo

- * o l-M CO

oo - ï r M rM

O o

CM 00 CM rM

O O

«tf 00 i n m

o o

CM rM OV l-M

i-M CM

CO rM CM CM

O O

O vo co i n

o o o o m o o

rM CO

tl > >-> <U rM

rH - - . 00

u a

CO r M CO CM

vj- VO • j - co co ~t

m vo CM CM

o

oo

o

vo

o

CM

CM

O l CM

O

m CM

o

00 l-M

O

00 m

o

o

CM

o -3-

O

CM 00

• * m O rM Ol CM CM Ol

oo co in in vo oi

o o o o o rM i n

m rM CM

o o

rM CO CM CM

O O

r - ov m m

o o

•tf vO r— 00

l-M rM

•tf m CM CM • « o o

oo oo rM CM

• • 1-M r M

«* f^

O

Ol r M

O

O vo

• O

co 1-M

CM

l-M CM

O

CM r -

l-M

w 4-> C cg

s 10 CU u •M

+ CM cu

fa • o a 10

+ co rH

< u t l

> o

•o cu 00 10 H V

> <

m

u a V

B Q t l U 4-1

+ CM 01

fn

•o d CO

a Pi

U <U

> 0

•a n 00

« u tu

> <

m 4-1 d

S a D u 4-1

+ CO r-l

< •a

a a

« Pi

U U

> 0

•o t l 00 10 IM tu

> < 91 A l Ul

120

3+ and other cations was not influenced by Al . A similar trend was found

2+ 2+ for N, Fe , and Mn in plants as the level of Fe in acid sulphate

floodwater increased (Table 4.5).

4.3.2.2 Second crop

The plant DM yields of different treatments for three soils are pre­

sented in Table 4.4. In general, DM yields were lower than the first

crop because of weather and of the cumulative effects of acid sulphate

floodwater prevailing during the first and second crops.

2+ At transplanting, low pH and high Fe in the soil solutions of Sina-

caban caused toxicities to rice plants. No significant difference in DM

yields was seen among treatment means (Table 4.4). The slight variation

in plant dry matter yield among treatments of Aparri acid sulphate

soils was due to i

the soil solutions

2+ soils was due to no marked difference in pH and Fe concentrations in

2+ In Aparri soil, the DM weight was not affected by the levels of Fe

2+ whereas the Fe treatment showed a sharp decrease in DM yield in

Ioloilo soils at 100 mg/1. A pH range from 3.5 to 5.9 alone did not

significantly affect the plant dry matter yield in Iloilo acid sulphate 2+

soils because at transplanting the Fe concentration in the soil so­lutions was less than 500 ppm (Fig. 4.3). Other treatments at Iloilo

2+ showed Fe toxicity symptoms a few weeks after transplanting because

of the high concentrations of iron in the soil solution. The DM yield,

therefore, dropped to minimal values.

The trend of the chemical compositions of plant materials was similar

to the first season (Table 4.6).

121

4.3.3 Quantitative relationship between acid sulphate floodwater

and plant dry matter yield

To quantify the yield reduction due to acid sulphate floodwater, yield 3+ 2+

was correlated with pH levels and concentrations of Al and Fe in

acid sulphate floodwater. Regression analysis for the first crop showed

that the DM yield could be expressed by the following equation:

Y = 36.12 - 9.49S - 0.035A1 - 0.015 Fe (R2 = 0.707)

where, Y is DM yield (g/pot), S is the dummy variable (S = 1, 2, 3 for 3+

Aparri, Iloilo and Sinacaban soils, respectively), Al is the concen-3+ 2+ 2+

tration of Al (mg/1), and Fe is the concentration of Fe (mg/1) applied in the acid sulphate flood water.

Plant DM yield was strongly influenced by soil type, and negatively 3+ 2+

correlated with Al and Fe concentrations in the acid water. A sepa­rate regression analysis was also performed for each soil during the

first crop. Negative correlation between DM yield and the concentration 3+ 2+

of Al and Fe was also found in Aparri and Iloilo soils:

Aparri: Y = 25.27 - 0.057 Al - 0.017 Fe (R2 = 0.707)

Iloilo: Y = 22.27 - 0.045 Al - 0.022 Fe (R2 = 0.844)

No correlation was observed for the Sinacaban soil.

During the second crop, DM yield data of Aparri and Iloilo soils were 3+ 2+

correlated. The variation of DM yield due to Al , and Fe concentra­tions in acid sulphate floodwater was:

Y = 23.62 - 7.67S - 0.022 AI - 0.006 Fe (R2 = 0.676)

This could be explained as a decrease in cumulative effects of Al and 2+

Fe in acid sulphate floodwater

solution reached limiting values.

2+ Fe in acid sulphate floodwater when the chemical compositions in the

122

Plant dry matter yield reduction due to aluminium and iron in acid sul­

phate flood water could be represented by:

Y = 6.14 - 0.022 Al - 0.011 Fe (R2 = 0.424) for Iloilo soil.

Because the acidity of acid sulphate floodwater is attributed to the 3+ 2+

presence of AI , Fe sulphates and free sulphuric acid, a single fac­tor was used to calculate the total acidity. The total acidity is the

+ 3+ 2+ sum in equivalent per liter of three ions: H , Al and Fe . Because

the temperature in the greenhouse was higher than outside, the évapo­

transpiration was assumed of 10 mm/day and 8 mm/day for the first and

second crops. Water added during the recycling fertilizers of the first

crop was 80 mm (or 1.5 liters). The cumulative acidity for first and

second crops was then calculated by multiplying the amount of added

acid sulphate floodwater and its chemical concentrations in equiva­

lents. This factor was used to correlate with the DM yield. Negative

correlation between total acidity and DM yield of Aparri and Iloilo

acid sulphate soils for the first crop was:

Y = 23.45 - 0.04 X (R2 = 0.742)

where y is the DM yield (g/pot) and X is the total acidity in equiv­

alents/1) for Aparri and Iloilo acid sulphate soils. Very poor corre­

lation was found for the second crop because high acidity and high Fe

concentration in the soil solutions resulted in poor yields. This

simple factor could be used to predict the yield reduction provided

that certain elements in soil solutions did not reach toxic levels.

4.4 Conclusions

On the basis of these findings the following general conclusions and

recommendations can be made:

1. The responses of three acid sulphate soils to added acid sulphate

floodwater were different in magnitude but similar in direction of

change of various chemical parameters.

123

2. pH alone did not affect the chemical changes of three acid sulphate

sulp 2+

3+ 2+ soils; Al or Fe in the acid sulphate floodwater produced low pH

and enhanced the solubility of Fe 3+

3. High Al concentrations in acid sulphate floodwater caused low pH 3+ +

in the solution through the exchange of Al and H in the clay

complex. 3+

4. Acid sulphate floodwater did not affect the concentration of Al

in the soil solution due to the high buffering adsorption capac­

ities of the soils.

5. pH levels of acid sulphate floodwater alone as low as 3.5 showed no

effect on the growth of rice at early stage. 2+ 3+

6. Plant DM yield was negatively correlated with Fe and Al con­

centrations in acid sulphate floodwater for the first and second

crops.

7. pH levels are not influenced by the chemical uptake of IR36 whereas 3+ 2+

the presence of high Al and Fe concentration in acid sulphate floodwater added to the soils enhanced the Al and N uptake and depressed the Mn.

3+ 2+

8. Concentrations of Al and Fe in the acid sulphate floodwater up

to 50 and 100 mg/1, respectively, did not directly influence the

growth of rice.

9. The one-time and cumulative effects of acid sulphate floodwater on

DM yield varied from soil to soil. + 3+ 2+

10. A single factor, total acidity, i.e. the sum of H , Al and Fë

in equivalents, could be used to determine the reduction in plant

DM yield provided that the chemical compositions of soil solutions

did not reach limiting toxicity values. The experiment was in the greenhouse where the hydrological factors

were limited. Field studies are therefore needed to investigate the

transformation of acid sulphate floodwater in soils and its influence

on rice yield.

126

effectiveness for a particular soil is determined largely by pH, P and

Ca concentrations in the soil solution (Peaslee et al., 1962, Ellis et

al., 1955, Khasawneh and Doll, 1978, Graham, 1955 and Howe and Graham,

1957). Many experiments have been conducted to determine the most

favourable soil and cropping conditions for its use. In general, ex­

perimental results have shown that rock phosphate is more effective on

acid soils than on neutral or alkaline soils (Peaslee et al., 1962,

Ensinger et al., 1967, Barnes and Kamprath, 1975). The use of acid-

forming N sources, or mixing elemental S with rock phosphate results in

the solubilization of appreciable amounts of P and, generally, in

better yields (Volk, 1944).

In acid sulphate soils (and acid lateritic soils), rice responded fa­

vourably to rock phosphates (Le van Can, 1982, La thi Hien and Vo tong

Xuan, 1979, and Misra and Panda, 1969). Incubating rock phosphate under

moist conditions for three weeks before transplanting produced better

rice yields than application just before transplanting (Shinde et al.,

1978).

Phosphorus deficiency is widespread in rice and other crops in many

tropical countries. Only nitrogen deficiency appears to be more exten­

sive. In acid sulphate soils, however, phosphorus is the main limiting

macronutrient for crop production.

Since the use of superphosphate is a luxury in many developing coun­

tries because of their limited foreign exchange, direct application of

ground rock phosphate from local deposits may be an economic alter­

native for P fertilization.

5.2 Objective

The objective of this study was to study the response of rice to dif­

ferent phosphate sources and fertilization methods on surface horizon

material of two acid sulphate soils.

127

5.3 Materials and methods

Material from the surface horizons of two acid sulphate soils, from

Iloilo and Malinao, The Philippines, was used in this experiment. Their

chemical properties are shown in Table 5.1.

Table 5.1 Some chemical characteristics of the two surface horizon

materials.

Chemical characteristics

pH of dry soil (1:1 H O )

ECe (mS/cm)

CEC (mmol/100 g)

organic C (%)

Total N (%)

Active Fe (%)

Active Mn (%)

Exch. K (mmol/100 g)

Exch. SO^" (%)

Olsen P (ppm)

Malinao

3.50

1.0

2.5

1.23

0.15

2.50

0.001

0.17

0.27

5.8

Material

Iloilo

3.90

8.49 (2.0)X)

30.9

1.55

0.11

3.0

0.001

-

-

2.0 (15.0)a)

1) First value for material as sampled; value in brackets for material

after leaching for 1 week.

The soil from Iloilo was leached with demineralized water to bring down

the salinity level. Two sources of 100 mesh rock phosphate were used:

Lumpoon from Thailand (5.8% P205) and North Carolina (30% P205) rock

phosphate.

Six kg soil was placed in a 12 litre plastic pot. All pots received

uniform rates of 50 ppm N and K as urea and potassium chloride. Then,

phosphate was applied (except to controls) and the soil was well mixed.

One set of triplicates was brought to 60-70% of field capacity, another

set to field capacity. These were incubated for three weeks. A third

set of triplicates was not incubated. The treatment combinations are

listed in Table 5.2.

128

Table 5.2 Treatment combinations of different phosphate rates and

fertilizing times and methods.

Fertilizing time and method

time before transplanting

water status 2/3 FC

3 weeks

1)

3 weeks

FC

1 day

flooded

P rate

source ppm P

control

02) SP

RP 3)

0

50

50

100

X

X

X

X

X

X

X

X

1) 2/3 FC: 60-70% of field capacity 2)

SP : superphosphate 3)

RP : rock phosphate

The soils in all pots were then flooded, pudded, left overnight and

four rice seedlings, 21 days old, cv. IR 36 were transplanted. After

30 days, two of the seedlings were cut and dried for chemical analysis.

At maturity, the other two plants in each pot were harvested and oven-

dry weights of grain and straw were recorded separately. Straw samples

were then ground for analysis of N, P, Fe and Al.

Treatments were completely randomized. The significance of differences

between treatments was analyzed by Duncan's Multiple Range Test.

5.4 Results and discussion

5.4.1 Effect of variation in phosphate rate, time of fertilizer

application and soil moisture status on pH of the soil

solution at transplanting and 6 weeks after transplanting

At transplanting, the pH of the soil solution varied only slightly

among the treatments (Table 5.3).

129

Table 5.3 pH of the soil solution at transplanting and 6 weeks after trans­

planting under different phosphate rates, time of application and

soil moisture status on two acid sulphate soils.

time before transplanting 3 weeks 3 weeks 1 day 3 weeks 3 weeks 1 day

water status 2/3 FC FC flooded 2/3 FC FC flooded

p

source

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

rate

ppm P

50

100

50

100

50

0

50

100

50

100

50

0

Iloilo

at transplanting

4.40

4.32

4.43

4.39

6 weeks

4.05

4.18

4.45

4.33

4.36

4.50

4.27

4.31

after

4.17

4.63

4.60

4.68

4.15

4.27

4.17

4.18

4.00

4.13

Malinao

4.15

4.30

4.32

4.43

transplanting

4.03

4.25

4.05

4.32

4.15

3.98

5-07

4.90

5.08

4.88

4.23

4.18

4.36

4.45

5.48

5.63

5.55

5.60

4.12

4.25

4.30

4.42

4.02

4.17

5.12

5.07

5.08

5.27

5.07

5.07

For each soil, values are not significantly different at 5% level by DMRT.

Six weeks later, the pH of the soil solution in the Iloilo soil had not

changed in spite of the submergence, except for a slight increase in

the rock phosphate treatments. The highest increase in pH of the

Malinao soil occurred in treatments where either of the two rock phos­

phates was incubated at FC for 3 weeks before transplanting

(Table 5.3), but even the control increased by 0.9 unit. This may be

attributed to the production of alkalinity by reductions during sub­

mergence.

130

5.4.2 Effect of variation in phosphate rate, time of fertilizer

application and soil moisture status on grain yield, straw

weight, plant height, tiller and panicle numbers

Without P fertilization, Iloilo soil produced a higher grain yield than

Malinao (Table 5.4). This was probably due to the high P availability

after leaching in the former soil (Table 5.1).

The response of rice to different phosphate rates and application time

varied between the two soils (Table 5.4). In the Iloilo soil, the grain

yield showed little response to rock phosphate fertilizer. Malinao

soil, however, produced the highest yields in treatments where either

of the rock phosphates was applied and the soil was kept at field

capacity for three weeks before transplanting (Table 5.4). The other

application methods (60-70% FC for three weeks, and one day before

transplanting) did not show good response to rock phosphate in Malinao

soil. Superphosphate was effective, however. In Malinao, there was a

significant increase in grain yield with increased application rate of

Carolina phosphate, but not of Lumpoon phosphate, in the treatments

kept at field capacity three weeks before transplanting.

Irrespective of source, RP application to Malinao soil at FC three

weeks before transplanting produced the highest straw weight, plant

height and number of panicles (Table 5.4): the same trends as in grain

yield.

The higher control yield in Iloilo soil corresponds to the higher

Olsen P value compared with Malinao. The lower maximum yields and the

lower response to all methods of P application may be related with the

persistently low pH, which remained about 4 to 4.5 even after 6 weeks

of flooding. In the Malinao soil, the pH had risen about one unit by

that time.

131

Table 5•4 Effect of variation in phosphate rate, time of fertilizer appli­

cation and soil moisture status on grain yield, straw weight, plant

height, tiller number and panicle number of rice plants at harvest

in two acid sulphate soils.

time before transplanting 3 weeks 3 weeks 1 day 3 weeks 3 weeks 1 day

water status 2/3 FC FC flooded 2/3 FC FC flooded

p

source

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

rate

ppm P

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

Iloilo

Grain yield (g/pot)

24.50 be 22.15 d

24.54 be 22.32 d

23.54 c 20.99 e

26.33 a 21.24 de

22.28 d

24.63 b

17.58 £

22.18 d

22.00 d

17.84 f

Straw weight (g/pot)

12.75 a 11.88 ab

12.18 ab 11.83 ab

12.40 ab 10.83 bc

13.91 a 11.78 ab

Plant heicht (cm)

80:6 d 80.1 d

80.9 d 80.5 d

85.0 c 76.9 ef

91.4 a 81.8 d

Tiller number

22.7 ab 20.3 c

24.7 a 20.7 bc

21.7 bc 21.3 bc

23.7 ab 21.7 bc

Panicle number

21.0 b 20.3 b

24.7 a 19.7 b

21.0 b 19.0 b

22.7 ab 20.3 b

11.14 ab

12.01 ab

9.96 bc

11.64 ab

12.24 ab

9.74 bc

76.0 ef

78.7 de

75.3 £

84.5 c

88.60 b

74.6 £

19.7 c

22.3 b

20.3 c

23.7 ab

24.6 a

19.3 c

19.3 b

20.3 b

20.0 b

23.7 ab

24.3 ab

18.7 c

Malinao

14.09 de

16.02 d

15.13 d

24.14 c

12.81 d

13.48 cd

12.00 de

14.78 bc

80.5 ef

83.8 d

82.2 de

84.5 cd

21.3 d

23.0 cd

18.7 e

22.0 d

21.0 ef

22.0 c

18.7 fg

20.0 f

28.89 b

35.44 a

32.91 a

33.38 a

13.58 cd

15.94 ab

15.02 ab

16.60 a

86.8 bc

89.0 ab

88.9 ab

89.8 a

28.7 b

32.0 a

27.0 b

30.0 a

27.3 b

30.0 a

24.7 c

28.0 b

12.08 e

14.18 de

14.78 d

13.06 de

29.06 b

11.34 e

10.64 f

11.02 ef

9.09 g

8.98 g

13.67 cd

7.50 h

69.3 h

70.5 h

78.8 f

76.0 g

88.3 ab

69.0 h

17.3 e

18.6 e

17.3 e

13.7 f

24.2 c

15.0 f

17.0 h

18.3 gh

15.0 k

13.0 1

23.7 d

15.0 k

For each soil, means having the same letter are not significantly different at

5 percent level by DMRT.

132

5.4.3 Effect of variation in phosphate rate, time of fertilizer

application and soil moisture status on the chemical compo­

sition of rice plants during the growing period

One month after transplanting

The concentration of N, Fe and Al in rice plants one month after trans­

planting showed little variation among the two soils and all treatments

(Table 5.5). Only in the Malinao soil, high Fe and Al concentrations

occurred in plants from the superphosphate treatment as well as the RP

treatment with incubation at FC for 3 weeks before transplanting. The

superphosphate treatment and most of the rock phosphate applications

with 3 weeks incubation resulted in increased P concentrations in

plants. Since P concentrations on Iloilo soil were of the same order as

on Malinao, and well above the deficiency range, the lower yields on

Iloilo cannot be ascribed to P deficiency in the fertilized treatments.

At harvest

In general, there was little variation in the N, Fe and Al contents of

straw at harvest on the Iloilo soil (Table 5.6). P concentrations in

straw after rock phosphate application at field capacity were higher

than in the other treatments. Concentrations of N, P and Fe in straw on

Malinao soil with rock phosphate were higher after incubation at field

capacity than at 60-70% FC; concentrations were erratic in treatments

without incubation.

5.4.4 Relative agronomic effectiveness of rock phosphate compared

with superphosphate

Table 5.5 shows the relative agronomic effectiveness of the different

treatments compared with a standard application of superphosphate. In

Iloilo soil, Carolina and Lumpoon rock phosphates incubated at 60-70%

FC for 3 weeks before transplanting were more effective than super­

phosphate. In Malinao soil, rock phosphate was superior over super­

phosphate only with incubation at field capacity. The RAE could be used

to calculate relative economic effectiveness once the price level of P

from the different phosphate sources is known.

133

Table 5.5 Effect of variation in phosphate rate, time of fertilizer appli­

cation and soil moisture status on the chemical composition of

rice plants on two acid sulphate soils, one month after trans­

planting.

time before transplanting 3 weeks 3 weeks 1 day 3 weeks 3 weeks 1 day

water status 2/3 FC FC flooded 2/3 FC FC flooded

p

source

Carolina RF

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

rate

ppm P

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

Iloilo

N (%)

3.96

4.01

3.83

4.00

P (W

0.29

0.35

0.41

0.49

3.58

3.74

3.55

3.83

0.33

0.36

0.42

0.43

Fe (ppm)

175

179

113

166

217

234

112

146

Al (ppm)

115

119

156

114

146

149

127

178

3.70

3.50

3.84

3.71

4.01

3.64

0.30

0.33

0.39

0.40

0.41

0.28

227

230

179

245

217

204

204

173

113

225

147

166

Malinac

3.28

3.40

3.62

3.57

0.29

0.32

0.32

0.34

213

263

306

243

121

140

395

457

3.16

3.46

3.44

3.37

0.28

0.31

0.35

0.33

333

394

339

370

324

431

336

349

2.98

3.20

2.94

2.77

3.67

3.16

0.29

0.26

0.29

0.29

0.40

0.28

229

217

249

247

338

253

223

243

124

164

343

272

134

Table 5.6 Effect of variation in phosphate rate, time of fertilizer ap­

plication and soil moisture status on the chemical composition

of straw at harvest on two acid sulphate soils.

time before transplanting 3 weeks 3 weeks 1 day 3 weeks 3 weeks 1 day

water status 2/3 FC FC flooded 2/3 FC FC flooded

p

source

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

Carolina RP

Lumpoon RP

superphosphate

control

rate

ppm P

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

50

100

50

100

50

0

Iloilo

N « )

0.85

0.98

0.98

0.93

P (%)

0.08

0.09

0.10

0.10

0.96

0.98

1.01

1.10

0.10

0.12

0.10

0.12

Fe (ppm)

344

361

321

341

358

368

354

460

Al (ppm)

58

85

60

92

73

83

71

86

0.84

0.87

1.03

1.05

1.05

0.95

0.08

0.08

0.10

0.10

0.10

0.09

243

273

331

327

338

332

75

87

85

82

79

96

Malinao

0.64

0.63

0.62

0.61

0.06

0.07

0.07

0.07

428

490

358

377

68

69

64

67

1.03

1.16

0.90

0.92

0.10

0.09

0.09

0.10

548

561

600

699

65

72

99

110

0.62

0.75

0.81

0.83

0.98

0.96

0.06

0.06

0.07

0.10

0.10

0.07

427

556

465

614

415

516

57

81

71

90

95

103

135

Table 5.7 Relative agronomie effectiveness1 of rock phosphate fertilizers

applied at different times and rates on soils with different

water status, compared with a standard superphosphate applica­

tion.

time before transplanting 3 weeks 3 weeks 1 day 3 weeks 3 weeks 1 day

water status 2/3 FC FC flooded 2/3 FC FC flooded

p

source

Carolina RP

Lumpoon RP

rate

ppm P

50

100

50

100

Iloi

160

161

137

204

lo

104

108

76

82

101

163

< 0

104

Mai

16

26

21

13

inao

90

136

122

124

4

16

19

10

1 Relative agronomic effectiveness:

Yield with rock phosphate treatment - control yield RAE = Yield with 50 ppm P as superphosphate - control yield

Values are means of triplicates.

x 100

5.5 Conclusions and recommendations

Based on the above findings, the following conclusions can be drawn.

1) Olsen P values in Iloilo soil increased after leaching excess salt.

Therefore, the Olsen P value for the non-leached, dry, saline soil

was a poor indicator for P availability.

2) Rice showed little response as the application rate of rock phos­

phate application increased from 50 to 100 ppm P.

3) Rice response to different phosphate fertilization methods varied

from soil to soil. Malinao soil produced the highest yield when rock

phosphate was applied 3 weeks before transplanting with incubation

at field capacity. Control yields on Iloilo soil were higher, but

maximum yields much lower than on Malinao soil.

4) The relative agronomic effectiveness of phosphate indicated that

rock phosphate was most beneficial in Iloilo soil with incubation at

60-70% FC for three weeks before transplanting and in Malinao soil

with incubation at FC.

These findings indicate that rock phosphate, properly incubated, could

136

be more efficient than superphosphate on acid sulphate soils. Field

experiments are needed to confirm or modify the following recommenda­

tions.

Incubation after rock phosphate application is quite feasible under

field conditions. Rock phosphate can be applied direct to the ploughed

field after harvesting a previous crop. These methods of rock phosphate

application followed by incubation could increase rice yields in P-

deficient acid sulphate soils and at the same time save the costs of

manufacturing water soluble phosphate fertilizers.

Questions remaining

The low maximum grain yields on Iloilo soil compared with Malinao are

not due to P-deficiency, since Olsen P values were higher than in

Malinao, and since P concentrations in plants at 6 weeks age as well as

in straw at harvest were similar on both soils and well above the de­

ficiency range.

The main difference observed between the two soils was the increase in

pH of the soil solution upon flooding. In Malinao, the pH rose to above

5 within 6 weeks, in Iloilo, the pH remained around 4-4.5. This would

suggest that acid, toxic compounds were not reduced at a sufficiently

fast rate in the Iloilo soil. Their identity is not known; however,

methods to increase the rate of pH rise after inundation would probably

be beneficial on Iloilo soil. Applications of manure or lime, even in

small doses, would create locally favourable conditions for microbial

activity and would presumably speed up the rise in pH.

Especially in Malinao, there are some indications for a positive re­

lation between grain yield in the fertilized treatments and Fe and Al

concentrations in plants one month after transplanting as well as in

straw at harvest. This is contrary to expectations at the start of the

experiment. The high Al concentrations are about 300 to 400 ppm, above

the 300-ppm toxicity limit suggested by Tanaka and Navasero (1966),

while grain yields from the same treatments are among the highest in

the experiment. The lower maximum yields on Iloilo soil are not associ­

ated with particularly high Al or Fe concentrations in the plants.

137

Acknowledgements

The author wishes to thank Dr. F.N. Ponnamperuma for his kindness in

providing the greenhouse space and facilities in the laboratory,

Dr. R. Brinkman and Dr. S.I. Bhuiyan for their valuable suggestions

during the course of these investigations.

5.6 References

Barnes, I.S. and E.J. Kamprath, 1975. Availability of North Carolina

rock phosphate applied to soils. Techn. Bull. 229, Agric. Exp. Stn.,

Raleigh, N.C., North Carolina.

Chien, S.H. and L.L. Harmond, 1978. A comparison of various laboratory

methods for predicting the agronomic potential of phosphate rocks

for direct application. Soil Sei. Soc. Am. J. 42: 935-939.

Ellis, R., Ir. M.A. Quader, E. Truog, 1955. Rock phosphate availability

as influenced by soil pH. Proc. Soil Sei. Soc. Am. 19: 484-487.

Ensinger, L.E., R.W. Pearson and H.W. Armiger, 1967. Effectiveness of

rock phosphate as a source of phosphorus for plants. U.S. Dep. Agric.

ARS: 41-125, Washington, D.C.

Graham, E.R., 1955. Availability of natural phosphorus according to

energy changes. Proc. Soil Sei. Soc. Am. 19: 26-29.

Howe, D.O. and E.L. Graham, 1957. Salt concentration: a factor in the

availability of phosphorus from rock phosphate as revealed by the

growth and composition of alfalfa. Proc. Soil Sei. Soc. Am. 21:

25-28.

Jackson, M.L., 1958. Soil Chemical Analysis. Chapter 7. Prentice Hall

Inc., Englewood Cliff, N.J.

Khasawneh, F.E. and E.C. Doll, 1978. The use of phosphate rock for

direct application. Adv. Agron. 30: 159-206.

La thi Hien and Vo tong Xuan, 1979. Ann huong phan Ian den nang suat

lua IR30 trong tren dat phu sa chua vung Can tho. (The influence of

P fertilizer on the yield of IR30 on acid alluvial soil in Can tho).

Khoa hoc ky thuat Nong Nghiep (Agric. Science and technique) No. 201,

Hanoi.

138

Le van Can, 1982. Rock phosphate in rice production on acid sulphate

soils in Vietnam. In: H. Dost (ed.). Acid sulphate soils. Proc. Int.

Symp. Wageningen. ILRI Pub. 31: 187-194.

Lehr, J.R. and Mc Clellan, G.H., 1972. A revised laboratory reactivity

scale for evaluation of phosphate rocks for direct application. Natl.

Fert. Dev. Cent., Bull. Y-43. TVA, Muscle Shoals, Ala.

Misra, V.K. and N. Panda, 1969. Evaluation of partially acidulated rock

phosphate in lateritic soil. Indian J. Agric. Sei. 39: 353-361.

Peaslee, D.W., C.A. Anderson, G.R. Burns and C.A. Black, 1962. Estima­

tion of relative value of rock phosphate to plants and different

soils. Proc. Soil Sei. Soc. Am. 30: 446-450.

Shinde, B.N., P.A. Sarangamath and S. Patnaik, 1978. Phosphorus trans­

formations from rock phosphates in acid soils and measures for in­

creasing their efficiency for growing rice (Oryza sativa L.). Plant

and Soil 49: 449-459.

Tanaka, A. and S.A. Navasero, 1966. Aluminum toxicity of the rice plant

under water culture conditions. Soil Sei. and Plant Nutr. 12 (2):

55-60.

Volk, G.W., 1944. Availability of rock and other phosphate fertilizers

and influence by lime and form of nitrogen fertilizers. J. Am. Soc.

Agron. 36, 46-56.

139

SIMULATION OF OXIDATION AND ACIDIFICATION PROCESSES IN ACID

SULPHATE SOILS

Abstract

Simulation models are useful to predict the effect of one or more of

the complex climatic, soil, water or chemical changes on the soil sys­

tem. Such predictions can be used to make economic evaluation of, for

example, the cost and benefit of reclamation work on acid sulphate

soils. The objective of this study was to develop a simulation model

to calculate the time course of acidity production from pyrite oxida­

tion in relation to the changes of ground water table, evaporation, en­

trance of oxygen and different chemical reactions. The model is based

on a multicompartment model in which the soil profile is divided

into a number of layers, is written in CSMP and contains three main

parts: INITITAL, DYNAMIC and TERMINAL. For each compartment of a clay

loam and a silty clay soil, the compartment thickness, its water con­

tent, pyrite content, cation exchange capacity, total cations, adsorbed

cations and oxygen concentrations are given as inputs. Three evapora­

tive demands of 4, 6 and 9 mm.d were used as a boundary condition at

the soil surface. These substantial differences in evaporative demands

lead to increasing water loss. Results show that the oxidation process

and the associated acidification of the soil are only marginally af­

fected by the different evaporative demands, although the oxidation

rate was very much influenced during the early part of the evaporation

process.

140

6.1 Introduction

Acid sulphate soils are derived from marine and estuarine sediments

containing high concentrations of reduced sulphur components, which

upon drainage and aeration, show oxidation of sulphides (mainly pyrite,

FeS„), which leads to a definite and severe acidification due to the

formation of sulphuric acid. Pyrite oxidation is a complicated process

which includes several types of oxidation-reduction reactions, hydro­

lysis and complex-ion formation, solubility controls and kinetic ef­

fects. The overall process describing pyrite oxidation is commonly

given by the following reaction:

FeS, + ^ 0, +1 H.O -• Fe(0H)„ + 2 H„S0, (6.1) ^(s) h 2(aq) l l (1) J(s) *(aq)

in which pyrite and water, in the presence of oxygen, form insoluble

ferric hydroxide and sulphuric acid. The quantity of acid products de­

pends on the rate of oxidation, which is controlled by climatological

and hydrological factors and soil properties. Many laboratory experi­

ments have been carried out to determine the rate of oxidation, the

acidification process, but models on pedogenesis have not received much

attention and have not been the object of research on acid sulphate

soils.

The composition of the soil solution as it moves through the soil, de­

pends on its pH, the anion content and the exchangeable base composi­

tion of the soil and reflects changes in the soil system. This composi­

tion, in turn, influences the effectiveness of the soil solution as

weathering agent. A model for predicting the rate of sulphate produc­

tion and the degree of acidity development and oxidation under differ­

ent and varying environmental conditions could be of importance for the

study of improvement of acid sulphate soils. The purpose of this study

is to develop and evaluate a computer simulation model for the oxida­

tion and acidification processes in acid sulphate soils. The model is

based on the moisture flow equation, calculated hydraulic conductivity

and suction functions, oxygen flow and cation exchange processes in the

soil. The water movement, oxygen movement and chemical processes sec­

tions are discussed separately before the presentation of the complete

model.

141

6.2 Oxidation process in acid sulphate soils

Investigations on pyrite oxidation usually focus on two main processes:

inorganic and microbiological oxidation processes. The microbiological

oxidation processes involve two main species of microbes: Thiobacillus

ferrooxidans and Thiobacillus thiooxidans. Thiobacillus ferrooxidans

was identified in acid mine waters (Leathen and Madison, 1949) and

later found to be capable of reducing ferrous iron under very acid con­

ditions. Thiobacillus ferrooxidans oxidizes ferrous iron, pyrite and

sulphur, whereas Thiobacillus thiooxidans oxidizes only sulphur and

pyrite. The inorganic oxidation process takes place in the presence of

water and oxygen. The pathways of pyrite oxidation are shown in

Fig. 6.1.

Fig. 6.1 The pathways of pyrite oxidation

inorganic processes

microbial processes

In this chapter the main emphasis will be on the inorganic oxidation

process. The amount of acid produced during the oxidation process de­

pends on the initial concentrations of the reaction products and on the

fate of iron sulphide. Four possible situations have been identified:

142

3+ 1. All iron is oxidized and remains in solution as Fe :

FeS2 + i| 02 + | H20 -• Fe3+ + 2 SO2" + H+ (6.2)

2+ 2. Iron is released as Fe :

FeS2 + | °2 + H 2 ° ~* F e 2 + + 2 S 0 4 _ + 2 H + ( 6 , 3 )

3. All iron is oxidized and hydrolyzed to iron (ferric) hydroxide:

FeS2 + i| 02 + | H20 -• Fe(OH)3 + 2 SO2" + 4 H+ (6.4)

ironlllhydroxide

4. Formation of jarosite:

FeS2 + ̂ <>2 + | H20 + | K+ -> | KFe3(S04)2(0H)6 + | SO2" (6.5)

jarosite + 3 H

The conspicuous deposition of hydrated ferric iron oxide and jarosite

in young acid sulphate soils suggests that the net result of pyrite

oxidation in sulphuric materials is represented by equations (6.4) and

(6.5).

The ferrous iron, hydrogen and sulphate ions released during pyrite

oxidation normally undergo various further reactions in the soil. Es­

sentially all ferrous iron is oxidized to ferric iron, which either

precipitates as ferric hydroxide, Fe(OH) , or jarosite, KFe_(S0,)„

(OH),. The larger part of the sulphate released during pyrite oxidation

remains in solution and is removed from the soil by leaching, and by

diffusion into the surface water if present. The remaining sulphate

partly precipitates, either as jarosite or as basic aluminium sulphate,

143

A1(0H)S0, (van Breemen, 1973) and is partly adsorbed, mainly by ferric

oxides. Under different weather and soil conditions, different products

of sulphate can be formed such as gypsum, [CaSO,*2H-0], sodium alum,

[NaAl(SO.) -1211.0], etc. Sulphate can be reduced again to sulphides,

which may temporarily be fixed as FeS in reduced conditions.

Many factors influence the rate of pyrite oxidation. Its rate-limiting

step in the soil is the supply of oxygen (van Breemen, 1973). The ef­

fect of oxygen concentration on oxidation rate is quantified differ­

ently among investigators. Using stability diagrams, van Breemen (1973) 3+

concluded that 0„ and Fe are the only two oxidants active in pyrite

oxidation under natural conditions. Some investigations (Hart, 1962;

van Breemen, 1973) indicated that the initial products of pyrite oxi-2+

dation are elemental S and Fe , while others (Garrels and Thompson, 2-

1960; Silverman, 1967; Bloomfield, 1972) reported that SO, is released 3+

almost instantaneously during pyrite oxidation to Fe . Elemental S is

formed at higher pH values in this oxidation pathway.

Van Breemen (1976) argues that in acid (pH < 4.4) oxidized environments

(Eh > 400 mV) jarosite is more stable than amorphous ferric oxide and

field observations confirm that the more severe the acidity, the more

dominant is jarosite deposition over iron oxide deposition.

Direct oxidation of pyrite by ferric iron with production of acidity

has been reported and is represented by the following equation (Singer

and Stumm, 1970):

FeS2 + 14Fe3+ + 8H20 ? 15Fe2+ + 2S0^~ + 16H+ (6.6)

When pH decreases to values below 4.5, ferric iron becomes more soluble

and begins to act as an oxidizing agent and below a pH of 3.0 it is the

only important oxidizer of pyrite. The presence or absence of oxygen

does not influence the oxidation rate by ferric iron (Singer and Stumm,

1970).

Other factors affecting the inorganic oxidation rate include tempera­

ture, surface area of pyrite, the presence of impurities such as trace

metals and the presence of other minerals such as chalcopyrite, sphale­

rite, calcite, etc.

Sveshnikov and Dobychin (1956) pointed out that rates of metal release

144

from different sulphides are related to their electrode potentials and

that a mixture of sulphides releases more metals into solution and de­

creases the pH more than mono-mineralic samples. The presence of rela­

tively inert conductors such as graphite has also been proposed to en­

hance the oxidation rate by increasing the electron flow between the

anodic and cathodic portions of an ore body (Cameron, 1979). Tempera­

ture causes the oxidation rate by oxygen to double for every 10°C rise

(Shumate et al., 1971).

These additional factors may or may not be important, depending on the

particular geological and weather conditions to which the oxidizing

pyrite is exposed. The surface area effects seem to be very important

in the initial stages of acid sulphate production, but as the pH de­

creases to 3 or less it seems to be less important. Pyrite can vary

significantly in grain size and morphology. Pyrite in coal deposits has

been found in at least six different forms, and the most reactive form

is framboidal pyrite consisting of pyrite crystals less than a micro­

meter in size (Caruccio et al., 1976). The occurrence of framboidal

pyrite has been used to estimate the acid forming potential of coal

refuse (Caruccio, 1975).

Several investigators have recognized a positive effect of smaller

particle size on pyrite oxidation rate (Quispel et al., 1952; Temple

and Delchamps, 1953; Hart, 1962). This effect has been attributed to

lattice defects (van Breemen and Harmsen, 1975) and to increased sur­

face area which increased reactivity (Stum and Morgan, 1970). Harmsen

et al. (1954) described soils containing significant amounts of pyrite

that had not acidified after drainage. They postulated that several

polysulphide fractions contributed to the stability of pyrite, but gave

no chemical or mineralogical evidence as support. Van Breemen (1973)

suggested that preservation was due to the large particle size (between

10 and 100 pm in diameter), combined with a relatively high pH. At

higher pH values, a protective coating of Fe„0„ may form on the pyrite

surface, thus slowing the oxidation rate. Harmsen et al. (1954) and

Quispel et al. (1952) reported that high levels of dissolved P strongly

depressed the decomposition of pyrite at pH values above 4 due to pre­

cipitation of iron as FePO,.

145

6.3 Computer simulation of the oxidation process

In the preceding section, the effect of various factors on the rate and

degree of pyrite oxidation was discussed. These factors in turn may be

affected by environmental conditions such as soil type and weather. If

all relevant relations can be formulated mathematically and if in addi­

tion these relations can be quantified, a model can be constructed de­

scribing the overall oxidation process in acid sulphate soils.

Computer simulation is the construction of mathematical models contain­

ing the essential features of a real system, the implementation of such

models on a computer (analog, digital, or hybrid), to arrive at a so­

lution and the study of the properties of such models in relation to

those of the real system; or "the building of a model and the study of

its dynamic behaviour". A model is a simplified representation of a

system, a limited part of reality with well-defined boundaries. A model

can be built if the structure of the system under consideration is suf­

ficiently understood, so that the various processes playing a role in

the system can be described mathematically. Simplification of the real

system is axiomatic in modelling, otherwise the system itself could be

used in the study; moreover, our understanding of reality is often

limited.

A simulation model represents the processes, which in reality proceed

continuously, in a series of discrete steps. The changes from one

moment to the next one are calculated taking into account all factors

that affect the system. The state of the system at any time can be

defined quantitatively by the values of the state variables and changes

in these states can be described mathematically.

The values of the state variables (mathematically represented by inte­

grals), such as the amount of water, the amount of oxygen and so on,

are known at any moment. The rate of change of each state variable is

determined by the state of the system and the environment, so that

rates are never mutually dependent. When all rates are calculated they

are realized over a short time-interval to arrive at the new values of

the state variables.

The simulation model is based on a multicompartment model, e.g. the

soil profile is divided into a number of layers (de Wit and van Keulen,

146

1972). Fig. 6.2 is a schematic representation of the soil profile, div­

ided into 20 compartments. For each compartment, the thickness of the

compartment, its water content, pyrite content, cation exchange capac­

ity, total cation content, adsorbed cations and oxygen concentration

are given as input at the onset of the calculations, as is the level of

the groundwater table (initialisation).

SOIL SURFACE -

DIFD(I) = 0.5» (TCOM(I-I) + TCOM(D)

DEPTH(I) =

DEPTHd-1) + DIFD(I)

RFLOW(I) = -EVAP0

_1 BOUNDARY! 1)

TC0M(1) _ _ { _ _ _ BOUNDARY(2)

J_DIFD(1)

I DIFD(Z)

COMPARTMENT!2)

RFLOW(I)

COMPARTMENT!I)

COMPARTMENT(N)

TC0M(2)

TCOK(I)

._L.

BOUNDARY(N+1)

RFL0W(N+1) DRAINAGE

Fig. 6.2 Geometry of the system and symbols used in the program for

the oxidation and acidification processes in acid sulphate

soils.

All characteristics of the soil that depend on the state of the system,

such as soil moisture suction and unsaturated conductivity for each

compartment, are derived in the model during the simulation from the

soil-specific functions relating these variables to moisture content.

Potential evaporation and rainfall are introduced as forcing functions,

that are not influenced by the behaviour of the system.

147

During the simulation, changes in soil moisture content and chemical

changes are calculated for each layer based on water balance and chem­

ical equilibria, respectively. Changes in groundwater table depth, fol­

lowing evaporation or rain are taken into account. The geometry of the

system and symbols used in the program for the oxidation and acidifi­

cation processes is represented in Fig. 6.2.

The program is written in CSMP (IBM, 1972) and contains three main

parts: INITIAL, DYNAMIC and TERMINAL.

All operations specified in the INITIAL part of the program are carried

out once prior to the actual simulation. All operations defined in the

DYNAMIC part are performed repeatedly for each elapsed time-interval

during the period of simulation. Integration is carried out by standard

system routines in CSMP. Finally, in the TERMINAL part calculations are

performed which are to be made only after the dynamic section has been

completed.

6.4 Water movement section

Water in the soil moves from points with a high potential (energy sta­

tus) to points with a lower potential. The total potential consists of

the matrix potential ip > also known as the capillary potential, the

gravity potential I|J and the osmotic potential, i|( :

i|j = tp + i|) + t|i ( 6 . 7 ) ^m T g T o

The potential is expressed as energy per unit mass of water, i.e. J/kg, 3

or as energy per unit volume of water, i.e. J/m or Pa. In hydrology,

hydraulic head (in m or cm water) is still often used. This quantity

is equivalent to 98.1 Pa (approximately 0.1 J.kg ) at the earth's

surface. In the following, we will express potential in terms of hy­

draulic head.

At the level of the groundwater table the matrix potential is zero. The

matrix potential is negative in unsaturated soil, i.e. above the

groundwater. The gravity potential is defined as the distance to a re­

ference level for which the groundwater table is chosen. Defining z as

148

150

The average conductivity is calculated as the arithmetic average of the

conductivities of the two compartments (de Wit and van Keulen, 1972):

KAV(N) = (K(N-l) + K(N))/2

The hydraulic conductivity of each compartment is obtained from an ex­

perimentally determined relation between conductivity and the volu­

metric water content of the compartment with:

K(N) = AFGEN (KTBN, WC(N))

The AFGEN statement provides linear interpolation in a given tabulated

function, entered in the program in the following form:

FUNCTION KTBN = (0.05, l.E-10), (0.10, l.E-5), (0.15, 5.3E-3), ...

This function presents the relation between the dependent variable, the

conductivity, the last number of each pair and the independent vari­

able, the volumetric water content, the first number of each pair. By

introducing different relations for different compartments it is pos­

sible to introduce a layered soil. The actual interpolation is then

most conveniently executed by the use of a TW0VAR function, which en­

ables the simultaneous use of water content and depth as independent

variables.

In the same way the matric suction of the compartment (SUCT(N), in m

H„0) is obtained from tabulated functions, which again may differ for

different compartments, with:

SUCT(N) = AFGEN (SUCTT, WC(N))

If a hydraulic head is present, the water in the soil may be above at­

mospheric pressure, but the relation between volumetric water content

of the soil and its matric suction is generally only given in the re­

gion below atmospheric pressure. The compressibility of water is so

low, that for a completely saturated soil the potential would increases

practically at an infinite rate with increasing water content. In prac-

151

tice, always some air is enclosed and compressed according to Boyle's

law. Hence, the suction curve may be extended in the region above

atmospheric pressure with a finite slope.

To arrive at the hydraulic potential (in m H„0), the gravity potential

must be added to the matrix suction. Thus:

P(N) = SUCT(N) + GRP(N)

The gravity potential is calculated with respect to the depth of the

groundwater table as :

GRP(N) = DPGWT - DEPTH(N)

where,

DPGWT = depth of the groundwater table in m

DEPTH(N) = the distance from the middle of the compartment to the soil

surface in m.

The flow rates over the first and the last boundary are defined differ­

ently, according to pre-defined boundary conditions. These may be any

time-dependent potential or flow rate. 3 -2 -1

The flow rate into the first compartment (FL0W1 in m m d ) equals the

rate of soil surface evaporation, EVAPO.

This rate is derived from the potential evaporation rate, calculated

from the equation developed by Jackson, 1973 and Jackson et al., 1973

as follows.

PET = AMAX1 (0.0, AMP * SIN (2.* PI * TIME/86400))

where,

AMP = rt times the average evaporativity AVPET, is defined as a fixed

value in the initial section.

The AMAX1 function takes the maximum value of the two arguments ; its

use in this statement prevents the potential evaporation rate from

152

becoming negative and sets the nighttime evaporation rate at zero. In

principle, the night-time evaporation rate can be set at any other

finite value or fraction of AVPET. Steady evaporativity such as may be

set in controlled conditions, can simply be simulated with the alter­

native statement:

PET = AVPET

The actual evaporation rate is set equal to the potential rate as long

as the matrix potential of the top compartment remains higher than the

initially specified air - dryness value, MINPOT:

IF (MPOT(l) . GT . MINPOT) EVAP = PET

After the top compartment has dried out to its minimum (air-dry) matric

potential, it can not loose any more water and the evaporation rate

becomes equal to the rate of transmission of moisture from the profile

(or to the potential rate, whichever is smaller):

IF (MPOT(l) . LE . MINPOT) EVAP = AMIN1 (PET, - RFL0W(2))

In either case,

RFLOW(l) = -EVAP

where,

RFLOW(l) = the flux of water through the soil surface.

The movement of the groundwater table resulting from changes in the

water content in the profile is based on the following assumptions

(Belmans et al., 1983):

If the groundwater level is set at a fixed value (controlled condi­

tions), a pressure head boundary condition at the bottom of the un­

saturated zone is used which is most conveniently placed at the bottom

of a compartment. In the case of a fluctuating groundwater level, the

size of the compartment situated just above the groundwater may vary

153

n-1

n

•

• n+1 0

•

T

•

m •

•

-

~AZn 1

AZn+1

AZn/2

AZn+2 =AZn-1

AZm =AJ

level

!n-1

groundwater

AZn-2 =AZn-1

AZn-1

Fig. 6.3 Illustration of the varying size (AZn) of the first unsatu­

rated soil compartment situated just above the groundwater

level.

(Fig. 6.3). It is equal to the distance between the groundwater level

and the bottom of the overlying compartment (AZn). The pressure head h

in the center of the compartment of flexible thickness n is at any mo­

ment considered to be in equilibrium with the groundwater level, i.e.

hn = AZn/2. Also the nodal point just below the groundwater table chan­

ges in position. This equilibrium procedure is followed to avoid in­

stability in computation, assuming that the equilibrium situation close

to the groundwater level does not deviate much from the real situation.

At each time step the water contents of all compartments in the unsatu­

rated zone are updated according to the equations given above, except

that of compartment n-1, which is maintained in equilibrium with the

groundwater level. Then the thickness and pressure head of compartment

n-1 are adjusted to the new groundwater level (equilibrium again).

The change in groundwater level is considered to occur as a consequence

of the transfer of water from the saturated to the unsaturated zone

(negative or positive).

154

The water balance of the soil profile can be written for each time step

as:

n DELW = I NFLW (I) x DELT

i=l

where,

DELW = change in water storage in the total soil profile.

If DELW is positive in the model, water has moved from the saturated to

the unsaturated zone in the soil profile which entails lowering of the

groundwater level. On the other hand, if DELW is negative there is a

rise in groundwater level.

On the basis of the value of DELW, at the end of each time step, a new

adapted groundwater level is calculated according to the following

procedure: If the absolute value of DELW exceeds 10 , then:

1. The groundwater level is lowered by a depth DELW.

2. The number of unsaturated compartments, n-1 determined.

3. The thickness Azn and equilibrium pressure head hn of compartment n

are calculated.

4. The pressure-head profile of the first four nodal points, i.e. the

first four compartments above the groundwater level is smoothed by a

redistribution procedure, taking as boundary conditions at the top a

flux equal to zero and at the center of compartment n, h = hn. The

"time" step used in this procedure is not real, i.e. simulation time

remains unchanged.

5. The change in water storage over the entire system is computed and

added to DELW, whose absolute value decreases.

If the absolute value of DELW

steps (1) to (5) are repeated.

If the absolute value of DELW < 10 the procedure stops; otherwise

6.5 Flow of oxygen in the soil profile

Oxygen movement in soils is mainly governed by two processes: mass flow

and diffusion flow. Mass flow is due to the difference in total gas-

pressure. In wet soils, for example, many air-filled pores are discon-

155

tinuous or blocked by water films and oxygen diffusion is slow. In

those cases, differences in total pressure may be sufficient to break

these films and cause some mass flow. Another form of mass flow is the

transfer of dissolved gases by rain or irrigation water percolating

into or through the soil. Water at 25°C, in equilibrium with air at

atmospheric pressure contains about 6 ml. 0„ per liter.

Diffusion is the transfer of gaseous molecules through porous media and

liquids at the same temperature and pressure under the influence of a

concentration gradient. The diffusion in one direction can be described

as:

F-A = & = - D £ - A (6.11) dt dx

where, -2 -1

F = rate of transfer per unit area of section (g.cm .s )

A = area (cm )

q = amount of gas (g)

t = time (sec) -3

c = concentration (g.cm )

x = distance along the line of flow (cm) 2 -2

D = diffusion coefficient (cm .s ).

The diffusion coefficient in soil is commonly given as the ratio D/Do, 2 -1

where D is the diffusion coefficient in soil (cm s ) and Do is the

diffusion coefficient of the same gas in air at the same temperature

and pressure. The ratio D/Do depends on soil properties only, notably

its pore geometry and not on the gas used for diffusion measurements

(Penman, 1940a; 1940b).

For a short range of Eg the relation between D/Do and gas-filled pore 3 -3

space Eg (cm air.cm soil) can be described by (Penman, 1940a;

1940b):

D/Do = 0.66 Eg (6.12)

Similar results were obtained by van Bavel (1952b) and Flegg (1953).

For a wider range of porosities, the following relationship is reported

156

by Currie (1960a,b):

D/Do = v EgM (6.13)

where,

Y and [l are coefficients determined from regression analysis.

Work on the ratio D/Do from different sources was reviewed by Bakker

and Hidding (1970). The relationship between D/Do and Eg used in our

model was based on the work of Leffelaar (1977).

The ratio D/Do for each soil compartment is obtained from a function

based on tabulated values of Fig. 6.4.

D/D0

0.18 -,

0.16

0.14

0.12

0.10

0.08 -

0.06

0.04

= po in t where 94.25 * of the aggregates are f i l l e d , and below which the i n t e r -aggregate pores s t a r t f i l l i n g

= in f luence on D/Dg mainly caused by aggregates

"p" = in f luence on D/DQ caused by in ter-aggregate pores

JL 0.2

f i l l i n g - « -

0.4 0.6 Eg (cm3-cm3)

drainage

Fig. 6.4 The relation between D/Do and gas-fil led porosity, Eg in an

aggregated soi l (Leffelaar, 1977).

157

DEFAC(I) = AFGEN (DEFACT, PVOL - WC(I))

where,

DEFAC = the diffusion efficiency factor.

The effective diffusion coefficient, DEF, is subsequently calculated

by:

DEF(I) = DZERO x DEFAC (I)

where,

DZERO denotes Do, the diffusion coefficient of oxygen in free air.

The average diffusion coefficient for flow between two adjacent com­

partments is calculated as:

ADEF(I) = (DEF(I) + DEF(I-l))/2

and the rate of oxygen diffusion is calculated similar to the rate of

water flow, from the diffusion coefficient and the gradient of oxygen

concentration in the two adjacent layers:

DFLOX(I) = ADEF(I) x (COX(I-l) - COX(I))/(0.5x(TCOM(I-l)+TCOM(I)))

The flow rates of oxygen over the first and the last boundary again

must be calculated in a different way. The flow rate into the first

layer, DFLOX(l), is greatly dependent on wether or not a water layer is

present on the soil surface. It is defined as:

DFLOX(l) = FCNSW (THWL,FLO,FLO,RDFLO)

FLO and RDFLO are defined by:

FLO = DEF(l) x (COUT - COX(1))/(0.5 x TC0M(1)) if THWL = 0

RDFLO = DZW x (COUT - C0X(1))/(THWL + NOT (THWL)) if THWL > 0

158

where,

COUT = the concentration of oxygen in the atmosphere

DZW = the diffusion coefficient of oxygen in water

THWL = the thickness of a water layer on top of the soil

NOT = a function that assumes the value 1 if the argument is smaller

or equal to zero and is otherwise zero. It is used to prevent by

zero division when no water layer is present.

Diffusion of oxygen into the soil profile is seriously impaired by the

presence of a water layer as the diffusion coefficient of oxygen in

A

water is about 10 times smaller than that in air. The rate of dif­

fusion of oxygen over the groundwater boundary is set to zero.

Mass flow of oxygen due to changes in soil moisture content in the

profile is calculated under the assumption that air moves in or out of

each compartment fully complementary with the water:

MFLOX(l) = NFLW(I) x COX(I)

Net flow of oxygen is finally calculated from the flow rates over the

upper and lower boundaries of a compartment, and the oxygen consumption

rate in that compartment.

NFLOX(I) = DFLOX(I) - DFL0X(I+1) - MFLOX(I) - RCOX(I)

RCOX is the consumption rate of 0. which is discussed in section 6.5.6.

6.5.1 The diffusion coefficient of oxygen in an aggregate, DCSPH

Lemon and Wiegand (1962) give the diffusion coefficient for oxygen in -5 2 - 1

free water as 2.6 x 10 cm .s at 25°C. The ratio of the diffusion

coefficient in a porous medium to that in a medium without any solid

obstacle, D/Do, equals 0.0566 for a porosity of 0.465 (Leffelaar,

1977).

Combining both values and converting to days, yields the diffusion

159

coefficient of oxygen in a water saturated aggregate:

D = 0.0566 x 2.6 x lu"5 x 86400 = 1.2715 lO"1 cm2.d_1

= 1.2715 x 10"5ra2d_1

6.5.2 The relative solubility of oxygen in water, SOLO

Grabble (1966) reports a value of 0.039 g 0„ l" water at 25°C and

1 bar pressure. Assuming 21% of oxygen in air, it follows that the con­

centration equals 0.21 x 1.3089 x lO-3 = 2.7487 x 10 g 02 cm"3 of

air. The relative solubility follows from the ratio of the amount of

;r -2

-3 -3 oxygen in water to that in air and amounts to 0.039 x 10 /1.3089 xlO = 2.9796 x 10

6.5.3 The critical concentration of oxygen, CCO

Greenwood (1961) reported respiration to be inhibited at an oxygen

concentration of about 7 x 10 molar. Conversion of this value to g

02 cm"3 of soil yields 7 x lu"7 x 32 x lO-3 = 2.24 x lO-8, a number

that was used by van Veen (1977).

6.5.4 Diffusion coefficient of oxygen in free air, DZERO

2-1 Grabble (1966), reported a value of 0.226 cm s at 25°C, equivalent to

2 -1 19626.4 cm .d . The oxygen concentration in free air, COVT, and the

diffusion coefficient in free water are given above, and are known

therefore.

6.5.5 The ratio D/Do for soil/air

The ratio D/Do gives the diffusion coefficient of molecules in a porous

system (D) compared to the diffusion coefficient in the same medium

160

(water or air) without any solid obstacle. Analytical solutions for the

description of soil aeration under uniform conditions have been given

by van Bavel (1951, 1952a) and Taylor (1949). Soil structure inevitably

causes heterogeneity in soils, a factor investigated by Bakker and Kid­

ding (1970) and Currie (1960a, 1960b, 1961a, 1961b). Currie presented

detailed results with respect to diffusion in systems having clear dis­

tinction between intra- and inter-aggregate pores, and carried out

measurements in both dry and wet materials.

In the present study the ratio D/Do is based on the calculation pro-

posed by Leffelaar (1977).

6.5.6 Oxygen consumption, RCOX

Oxygen is consumed by root respiration if plants are present, by micro-

biol respiration and by pyrite oxidation. Grable (1966) reported values -2 -1

for oxygen consumption ranging from 5 to 10 l.m .d . Bakker and Hid-

ding (1970) reported the highest value of Grable for only microorgan--2 -1 -1

isms (± 8. 9 1.0 m . 25 cm depth .d ) . Furthermore, Woldendorp

(1963), showed that ratio of respiratory activity roots to microorgan­

isms was about 2 to 1. This world imply that the highest reasonable -2

estimate of oxygen consumption may be about 26.67 1.0. m . 25 cm -1 -1 -1

depth depth d

The model assumes that 40 percent of the oxygen entering the pyritic

layers is consumed by pyrite oxidation.

6.5.7 The sulphate production, (PSO,) and the acid production,

RHYD

The sulphate production depends on the amount of oxygen and is cal­

culated from equation (6.2). The amount of sulphate is equal to 192 2 jTjr g 0. = 1.6 g 0 and the acid production is equal to rr g SO, = 0.0208 g SO,.

161

6.6 Transport of cations in the soil profile

In this section the cation exchange processes and the movement of dif­

ferent cations is treated. In most soils, a considerable amount of im­

mobile negative charges is present. These charges are associated with

the presence of clay particles and organic matter particles. In the

case of the clay particles these negative charges are the result of

processes that occurred during the formation of their lattice, con­

sisting of SiO, and A10,(0H) configurations. In part of the lattice

the Si and/or Al ions have been replaced by cations of lower valence

because the Al- and Si-atoms were not present in the required ratio. A

direct consequence of this substitution is a deficit of positive charge

in the lattice.

Because electroneutrality must be maintained, these deficits in the

lattice are compensated by the absorption of positive ions on the sur­

face of the lattice. These ions, however, may be exchanged with other

positive ions in the soil solution. This exchange process is very

rapid, so that it may be assumed in general that at any moment equilib­

rium exists between the concentration of the various positive ions in

the soil solution and those adsorbed on the soil matrix.

Because the composition of the soil solution may change as a result of

the processes associated with the oxidation of pyrite, and transport

due to mass flow and diffusion, a quantitative description of the ex­

change process is necessary.

The total negative charge of the soil matrix is termed the CEC, or ca­

tion exchange capacity, and is commonly expressed in meq. per 100 grams

of dry soil material. Its value is determined by the combined effect of -2

the charge per unit of area (surface density of charge in keq m )

which is a function of clay type and the area per unit of weight (spe-2 -1

cific surface area in m kg ) which is a function of clay type and

main constituent ion.

In this chapter the cations H , Ca , Al , K , Na , Mg are included

in the model, instead of only the few cation exchange reactions that

have traditionally been considered in simulation studies of salt trans­

port.

162

6.7 Calculation of the composition of the exchange complex and

the soil solution for five cations

To calculate the distribution of ions between the solution and the ad­

sorption complex, the equilibria between the cations in solution and

the exchangeable cations for the various combinations is defined as:

E2 1" =Y1 NaV <«•») sol ads

Mg n Mg .

err =h erf «•"> sol ads

Ca , Ca .

» S o l * <»•.*>

sol ads

Al , Al ,

- ^ - ^ Y . - ^ H T C6.17) "•..Z (Naads)

The subscripts sol and ads refer to the dissolved and adsorbed frac­

tions, respectively.

Y , Y„, Y-, Y, and Y„ are the exchange constants for the respective

cation pairs which are introduced in the model as fixed values; they

include the activity coefficients of the ions in solution. 3

All concentrations are expressed in eq/m .

The sum of the concentrations of the six adsorbed cations must be equal

to the cation exchange capacity in each layer according to:

H . + Na . + K . + Ca . + Mg , + Al . = CEC (6.18) ads ads ads ads ads ads

163

In the model, the CEC is a variable which is a function of depth only

and is independent of pH and complex composition. If K , Ca ,

Na , MR , H ^ and Al^ ,_ are used for the total amounts of the tot' 6tot' tot tot

various cations (solid + liquid phase) and X, = Na ,/Na . , then v ^ r 1 sol ads

equations (6.13) to (6.15) can, after rearrangement, be substituted

in equation (6.18):

C F C - Ütot + A o L - Ht Q t Catot Mgtot C E C - 1 + Y X l+XlYl l+XlY4 1 + x 2 . 3 1 + X 2 Y 2 Ï 3

+ — ^ - (6.19) 1+Y1Y5

As the rate of exchange is high compared with the rates of diffusion,

dispersion and water flow, Eqn. (6.19) is used to calculate for any

compartment the distribution between adsorbed ions and ions in solu­

tion.

X. is found from Eqn. (6.19) by a method of successive better approxi­

mations using the Newton-Raphson method as elaborated in the IBM-SSP

subroutine RTNI, modified to facilitate the choice of a correct initial

value for the iterative procedure.

Substitution of the value of X.. in Eqns. 6.13 through 6.17 provides the

values for Na . , K , , Ca , , H , , Mg _ , Al . , Na , , K , , Ca . , sol' sol' sol' sol' °sol' sol' ads ' ads' ads'

ads' ads ads'

The use of subroutine RTNI is explained in detail in the IBM Program­

mers' Manual (1968). Only some salient points are highlighted here. The

subroutine refines the initial guess XST of a root of the general non­

linear equation f(x) = 0 according to Newton's iteration scheme:

f(x.)

V i = xi • FIxTT (i = °'1'2-i

Each iteration step requires one evaluation of f(x) and one evaluation

of f'(x). Both f(x) and f ' (x) are calculated in an externally added

subroutine CAT, where f(x) is defined by FF:

164

FF = CEC Natot , Ktot , Htot , Catot 1+Yl 1+XlYl 1+X1Y4 1+X2y3

A1tot

1+X1Y5

, M*tot

1+XÎY2Y3

(6.20)

f'(x) is the first derivative of FF with respect to x and is defined as

DERF in the model.

The expression for DERF is rather long, therefore the reader is re­

ferred to the listing of subroutine CAT. Within subroutine RTNI, sub­

routine CAT is called by the dummy name FCT. In the original version of

RTNI, the iteration procedure is terminated if a prespecified error

criterion, controlled by EPS, is satisfied. If after a preset number of

iterations the error criterion is not satisfied, the iteration ends

with an error return (1ER = 1).

If the error criterion is not satisfied within the number of iterations

permitted, a new round of iterations was started, allowing for less

accurate results. This is achieved by increasing EPS by a factor of 10;

if necessary, this can be repeated once more, resulting in a maximum

increase in EPS by a factor of 100. The indicator IEPS records how many

times this feature is used.

A second feature that was introduced is a correction for those situa­

tions where the adjustment factor f(x.)/f'(x.) is greater then x., or

in the symbols of the routine RTNI, if DX is greater than X. This may

be so if the first guess of X is too far out. Then, arbitrarily, DX is

reduced to 0.9 x DX, which is repeated until a value is reached where

DX is less than X.

Usually this procedure works quite well and allows normal termination

of the iteration. If the decrease in DX is still required for the last

iteration step (I = 20), the routine does not provide a solution due to

insufficient convergence. Then the iteration is terminated, and the

error indicator 1ER is set to 4. The call of RTNI results normally in a

value for z (ratio Na ,/Na , ) and values for the indicators 1ER, I, sol ads ' '

IEPS. The last three are not further used in the model, but during

debugging stages they are used to trace malfunctioning of the sub­

routine .

165

6.8 Calculating cation transport in the soil profile

The basis of all calculations of transport of substances in soil is the

law of conservation of mass. For one-dimensional flow with a uniform

macroscopic flow velocity, the conservation equation may be written as:

2 3si 3ci _ _. 3 ci „. 3ci . ,c 01^ §T + BT = Dl TT " Vl BT + h ( 6-21)

3x

where,

ci = the concentration of solute i in solution expressed as mass of

solute per unit volume of solution

si = the concentration of solute i in the soil solution associated with

the adsorbed phase

Di = the apparent diffusion coefficient of the solute

Vi = the average interstitial velocity of the solution

<|>. = the production term, i.e. the net rate at which the mass of solute

i is produced per unit volume of solution due to a specific trans­

formation.

In the present model the production term is calculated for acid only,

based on equation (6.2).

The production of acid resulting from pyrite oxidation is calculated

as:

RPHYD (I) = PS04 (I) x 0.0208

and PS04 (I) = RFLOX (I) x 1.6

based on the assumption that the products of pyrite oxidation are

mainly ferric hydroxide, Fe(OH)-, and sulfuric acid, H_S0,.

The rate of flow of a chemical substance from one compartment to the

next one is equal to the product of the concentration in solution and

the flow rate of the solution (mass flow), plus the flow rate due to

diffusion and dispersion.

166

The mass flow of a given ion is assumed to take place from the middle

of one compartment to the middle of the adjacent one. To avoid the

phenomenon of mathematical dispersion, the concentration used in the

calculation is obtained by averageing the concentrations of the two

compartments (Goudriaan, 1973).

For each cation the concentration is calculated from the amount in each

compartment with:

CX(I) = CXSA/WC(I)

where,

X stands for the acronym of each of the six relevant cations.

Mass flow over the Ith boundary (Fig. 6.2) is then for each cation re­

presented by:

MFLX(I) = RFLOW(I) x.5x(CX(I)+CX(I-l))

The transport of ions by diffusion is proportional to the concentration

gradient and to the diffusion coeffient. The latter is smaller in soils

than in pure water, because only part of the volume is occupied by wa­

ter. Moreover, the soil pores form a labyrinth, hence the ions have to

traverse a longer path than the distance between two points. The dif­

fusion coefficient in water is therefore multiplied by the volumetric

water content and a tortuosity factor. The latter is also a function of

the water content, but so little is known quantitatively about this

relation, that it is generally assumed to be a constant, having a value

between •Jz and -J3. In addition to the "pure" diffusion flow there is

dispersion of the solutes as a result of the velocity distribution of

the solution in pores of different size. This dispersion flow is also

proportional to the concentration gradient and the proportionality

factor is the product of the average flow rate of the solution and a

dispersion factor. The latter has a value ranging from 0.7 for coarse

sands to 7 for loamy soils (Frissel et al., 1970).

To describe the diffusion flow for each of the cations, first the ap­

parent diffusion coefficient is defined:

167

APDIFX(I) = (DNOTXxWC(I)xTORT+RFLOW(I)xDISP)/DIFD(I)

where, 2 -1

DNOTX = diffusion coefficient (m .d )

TORT = tortuosity factor (unitless)

DISP = dispersion factor (m)

and subsequently the flow rate is defined by:

DFLH (I) = APDIFX(I)x(CHYD(I-l)-CHYD(I))

The mass flow and diffusion flow of cations over the upper and lower

boundary of the soil profile are assumed to be zero.

The net flow of each cation is calculated with:

NFLX(I) = MFLX(I)-MFLX(I+1)+DFLX(I)-DFLX(I+1)

Only in the case of hydrogen a slightly different formulation is used,

to account for its production in the oxidation process:

NFLHYP(I) = MFLH(I)MFLH(I+1) + RPHYD(I)

The integration is carried out with:

AX = INTGRL (TXI, NFLX, 20)

In the present model the rectilinear integration routine is used, with

a time step of 0.001 day.

6.9 Results and discussion

It appeared impossible at this stage to obtain sufficient accurate data

for calibration and validation of the model.

To test the performance of the model, therefore, some sensitivity tests

were carried out. These were directed at testing the effect of differ-

168

ent soil types and various evaporative demands on model output relevant

to the acidification process.

Two soil types were tested, a clay loam and a silty clay. Hydraulic

properties of the two soil types were derived from Rijtema (1969) using

semi-empirical relations between soil suction and hydraulic conductiv­

ity. The resulting functions are given in tabulated form in the listing

of the model (Appendices 6.1 and 6.2). For both soil types runs were

made with evaporative demands of 4, 6 and 9 mm.d , introduced as for­

cing functions.

In all cases the profile started at an equilibrium situation, assuming

an initial groundwater table at 0.3 m below soil surface. The moisture

contents at saturation for clay loam and silty clay are 0.445 and 0.504 3 -3

cm .cm , respectively.

The distribution of soil moisture in the profile after 5, 10 and

30 days of evaporation at the three evaporativities is shown in

Fig. 6.5. As can be expected, the soil moisture content of the surface

layers decreases with the increasing evaporative demand.

After 30 days of evaporation, when the soil has started to dry up at

the surface, the difference in soil moisture in the top layers for

three evaporation rates becomes small (Fig. 6.6). The cumulative water

losses are 80, 90 and 92 mm for evaporative demands of 4, 6 and

9 mm.d respectively (Fig. 6.7). Hence, despite more than a factor 2

difference in evaporative demand, there is only 15 percent difference

in cumulative evaporation, because of the difference in drying out of

the top layers and its depressing effect on soil surface evaporation.

As the topsoil dries out, transport of water from the profile to the

atmosphere is increasingly hampered and the evaporation rate declines.

The dry surface acts as a barrier to further evaporation (mulch

effect).

The simulated distribution of soil moisture in the profile for the two

soils is given in Fig. 6.8. Higher moisture contents are found in silty

clay.

169

O ., 20 30 40 50 60 Hl 1 1 T 1

0.5

1.0

Evaporation

• - # 4mm/day

A - A 6mm/day

O-O 9mm/day

5 days

moisture c o n t e n t ( ï )

20 30 40 50 60

depth(m)

Fig. 6.5 The distribution of soil moisture at different depths along

the profile of a clay loam soil under three evaporation

rates.

moiture content!*)

60

moisture content(%)

f i rs t layer

Evaporation

• - • 4mm/day

A-A 6mm/day

O-O 9mm/day

40

30

20

10

^ ^ -^ ^ f c & q

second layer

i

H » • ,. $=$s=&4

•-• A-A

O-O

Evaporation

4mm/day

6mm/day

9mm/day

30

days

20 30

days

Fig. 6.6 The changes of soil moisture of the first and second layers

with time under different evaporative demands for clay loam

soil.

170

Evaporation

•—• 4mm/day

&-& 6mm/day

O-o 9iran/day

20 30 days

Fig. 6.7 The cumulative evaporation under three evaporation rates for

clay loam soil.

20 30 40 50

0.5

1.0

O-O clay loam

•-• silty clay

0 day

moisture contentful

20 30 40 50

depth (IP)

Fig. 6.8 The moisture content of different depths for two soil types

after 0, 5 and 10 days of evaporation (6 mm/day).

171

Table 6.1 The concentration of 0„ in clay loam over time at an evapo­

rative demand of 4 mm/d.

days

depth

(cm)

0- 5

5- 10

10- 15

15- 20

20- 25

25- 30

30- 35

35- 40

40- 45

45- 50

50- 55

55- 60

60- 65

65- 70

70- 75

75- 80

80- 85

85- 90

90- 95

95-100

2

2

2

2

2

2

0

0

0

0

0

0

3

E-

E

E-

E-

E-

E-

-4

-4

-4

•4

-4

•4

2.0

2.0

1.8

1.5

1.1

5.7

2.8

6.6

1.0

1.1

8.6

5.6

2.6

E-4

E-4

E-4

E-4

E-4

E-5

E-8

E-12

E-15

E-19

E-24

E-28

E-32

10

2.0

2.0

1.8

1.5

1.1

5.7

6.3

3.2

1.0

2.4

7.3

1.2

1.6

E-4

E-4

E-4

E-4

E-4

E-5

E-8

E-ll

E-14

E-18

E-22

E-25

E-29

20

2.1

2.0

1.8

1.5

1.1

5.7

1.3

1.4

9.6

4.8

1.9

5.8

1.5

3.2

E-4

E-4

E-4

E-4

E-4

E-5

E-7

E-10

E-14

E-17

E-20

E-24

E-27

E-31

30

2.1 E-4

2.0 E-4

1.8 E-4

1.5 E-4

1.1 E-4

5.7 E-5

1.5 E-7

3.2 E-10

3.4 E-13

2.6 E-16

1.6 E-19

7.5 E-23

3.0 E-26

1.0 E-29

The simulated time course of concentration of 0. at different depths

in the profile is given in Table 6.1 for the clay loam. As evaporation

proceeds, the depth of the groundwater increases, the moisture content

in the profile decreases and oxygen has the opportunity to enter the

unsaturated layers of the soil profile. The increase in overall oxygen

concentration is the result of a higher proportion of air filled pores

in the soil. There is hardly any difference in oxygen concentration

174

3 Table 6.3 The production of sulphate (kg/m ) in clay loam soil (SUCT ,

COND.) at different evaporation rates.

days 5 days 10 days

EV(mm/day) 4 6 9 4 6 9

depth

(cm)

0- 5

5- 10

10- 15

15- 20

25- 30

30- 35 8.1 E-12 8.3 E-12 1.0 E-ll 1.2 E-ll 1.7 E-ll 1.6 E-ll

35- 40 4.3 E-15 6.9 E-15 7.0 E-15 1.6 E-14 1.9 E-14 1.9 E-14

40- 45 9.8 E-19 1.3 E-18 1.5 E-18 6.9 E-18 9.5 E-18 8.7 E-18

45- 50 1.4 E-22 1.7 E-22 2.1 E-22 2.1 E-21 2.6 E-21 2.5 E-21

50- 55 1.4 E-26 1.6 E-26 2.1 E-26 4.4 E-25 5.5 E-25 5.7 E-25

55- 60 9.9 E-31 1.1 E-30 1.6 E-30 7.2 E-29 8.7 E-29 9.4 E-29

60- 65 5.6 E-35 6.6 E-35 9.8 E-35 9.3 E-33 1.1 E-32 1.1 E-32

65- 70 9.9 E-37 1.1 E-36 1.3 E-36

70- 75

75- 80

80- 85

85- 90

90- 95

95-100

only marginally affected by different evaporative demands.

The model presented in this chapter is only a first step towards the

development of a truly comprehensive model for the oxidation and acidi­

fication processes in acid sulphate soils, that could eventually be

used to formulate recommendations for management and reclamation of

these soils.

175

Evaporation #-• 4mm/day A-Vi 6mm/day 0-0 9mm/day

depth(m) depth(m)

Fig. 6.10 The concentration of hydrogen at different depths under

three evaporation regimes after 10 and 50 days of evapora­

tion for clay loam soil.

6.10 References

Bakker, J.W., and A.P. Hidding, 1970. The influence of soil structure

and air content on gas diffusion in soils. Neth. J. Agric. Sei. 18:

37-48.

Bavel, C.H.M. van, 1951. A soil aeration theory based on diffusion.

Soil Sei. 72: 33-46.

Bavel, C.H.M. van, 1952a. A theory on the soil atmosphere in and around

a hemisphere in which soil gases are used and released. Proc. Soil

Sei. Soc. Am. 16: 150-153.

176

Bavel, C.H.M, van, 1952b. Gaseous diffusion and porosity in porous

media. Soil Sei. 73: 91-104.

Belmans, C., J.G. Wesseling and R.A. Feddes, 1983. Simulation model of

the water balance of a cropped soil: SWATRE. J. Hydrol. 63: 271-286.

Bloomfield, C., 1972. The oxidation of iron sulphides in soils in re­

lation to the formation of acid sulphate soils, and of other deposits

in field drains. J. Soil Sei. 23: 1-6.

Breemen, N. van, 1973. Soil forming processes in acid sulphate soils.

In: Dost, H. (ed.), 1973. Proc. Int. Symp. on Acid Sulphate Soils.

Wageningen, International Institute for Land Reclamation and Improve­

ment, Publication 18, vol. I. pp. 66-130.

Breemen, N. van, 1976. Genesis and solution chemistry of acid sulphate

soils in Thailand. Ph.D.Thesis, Agricultural University, Wageningen.

263 pp.

Breemen, N. van and K. Harmsen, 1975. Translocation of iron in acid

sulphate soils. I. Soil morphology, and the chemistry and mineralogy

of iron in a chromosequence of acid sulphate soils. Proc. Soil Sei.

Soc. Am. 39: 1140-1148.

Cameron, E.M., 1979. Effect of graphite on the enhancement of surficial

geochemical anomalies originating from the oxidation of sulphides. J.

Geochem. Expl. 12: 35-43.

Caruccio, F.T., 1975. Estimating the acid potential of coal mine re­

fuse. In: M.J. Chadwick and G.T. Goodman (eds.). The ecology of re­

source degradation and renewal. Blackwell Sei. Pub., London, pp. 197-

205.

Caruccio, F.T., G. Geidell and J.M. Sewell, 1976. The character of

drainage as a function of the occurrence of framboidal pyrite and

groundwater quality in eastern Kentucky. In 6th Symp. Coal Mine

Drainage Res., Louisville, Ky. pp. 1-16.

Currie, J.A., 1960a. Gaseous diffusion in porous media. Part I. A non

steady state method. Brit. J. Appl. Phys. 11: 314-317.

Currie, J.A., 1960b. Gaseous diffusion in porous media. Part II. Dry

granular materials. Brit. J. Appl. Phys. 11: 318-324.

Currie, J.A., 1961a. Gaseous diffusion in the aeration of aggregated

soils. Soil Sei. 92: 40-45.

177

Currie, J.A., 1961b. Gaseous diffusion in porous media. Part III. Wet

granular materials. Brit. J. Appl. Phys. 12: 275-281.

Currie, J.A., 1965. Diffusion within minostructure, a structural para­

meter for soils. J. of Soil Sei. 16: 2: 279-289.

Flegg, P.B., 1953. The effect of aggregation on diffusion of gases and

vapours through soils. J. Sei. Food and Agri.x 4: 104-108.

Frissel, M.J., and P. Reiniger, 1974. Simulation of accumulation and

leaching in soils. Wageningen centre for Agricultural Publishing and

Documentation. 116 pp.

Frissel, M.J., P. Poelstra and P. Reiniger, 1970. Chromatographic

transport through soils. Plant and Soil 33: 161-176.

Garrels, R.M., and M.E. Thompson, 1960. Oxidation of pyrite in ferric

sulphate solution. Am. J. Sei. 258: 57-67.

Goudriaan, J., 1973. Dispersion in simulation models of population

growth and salt movement in the soil. Neth. J. Agric. Sei. 21:

269-281.

Grabble, A.R., 1966. Soil aeration and plant growth. Adv. Agron. 18:

57-106.

Greenwood, D.J., 1961. The effect of oxygen concentration on the decom­

position of organic materials in soil. Plant and Soil 14: 360-376.

Harmsen, G.W., A. Quispel and D. Otzen, 1954. Observations on the for­

mation and oxidation of pyrite in the soil. Plant and Soil 5:

324-348.

Hart, M.G.R., 1962. Observations on the source of acid in empoldered

mangrove soils. I. Formation of elemental sulphur. Plant and Soil 17:

87-98.

IBM, 1968. System/360. Scientific Subroutine Package (360A-CM-03x)

version III, Programmers' Manual.

IBM, 1972. Continuous System Modelling Program III (CSMP III). Program

Reference Manual, Program Number 5734-XS9. 186 pp.

Jackson, R.D., 1973. Diurnal changes in soil water content during dry­

ing. In "Field water regimes". Soil Sei. Soc. Am., Madison, Wiscon­

sin, pp. 37-55.

Jackson, R.D., B.A. Kimball, R.J. Reginato and S.F. Nakayama, 1973.

Diurnal soil water evaporation: Time-depth-flux patterns. Soil Sei.

Soc. Amer. Proc. 37: 505-509.

178

Keulen, H. van and CG.E.M. van Beek, 1971. Water movement in layered

soils. A simulation model. Neth. J. Agric. Sei. 19: 138-153.

Leathen, W.W. and K.M. Madison, 1949. The oxidation of ferrous iron by

bacteria found in acid mine water. Soc. Am. Bact. , Abstracts of pa­

pers, 64.

Leffelaar, P.A., 1977. A theoretical approach to calculate the an­

aerobic volume fraction in aerated soil in view of denitrification. A

computer simulation study. Report no. 9. Department of Theoretical

Production Ecology, Agricultural University Wageningen, The Nether­

lands. 96 pp.

Lemon, E.R., and C.L. Wiegand, 1962. Soil aeration and plant root re­

lations II. Root respiration. Agron. J. 54: 171-175.

Penman, H.L., 1940a. Gas and vapor movement in the soil. Part I.

J. Agr. Sei. Camb. 30: 447-462.

Penman, H.L., 1940b. Gas and vapor movement in the soil. Part II.

J. Agr.Sei.Camb. 30: 570-581.

Quispel, A., G.W. Harmsen and D. Otzen, 1952. Contribution to the chem­

ical and bacteriological oxidation of pyrite in soil. Plant and Soil

43: 43-55.

Rijtema, P.E., 1969. Soil moisture forecasting. Nota 513. I.C.W.,

Wageningen, the Netherlands, 28 pp.

Silverman, M.P., 1967. Mechanism of bacterial pyrite oxidation. J. Bac-

teriol. 94: 1046-1051.

Singer, P.C. and W. Stumm, 1970. Acid mine drainage: the rate/determ­

ining step. Science 167: 1121-1123.

Stum, W. and J.J. Morgan, 1970. Aquatic Chemistry - John Wiley, New

York, 583 pp.

Sveshnikov, G.B., and S.L. Dobychin, 1956. Electrochemical solution of

sulphides and dispersion aureoles of heavy metals. Geokhimiya 4:

413-419.

Taylor, S.A., 1949, Oxygen diffusion in porous media as a measure of

soil aeration. Proc. Soil Sei. Soc. 14: 55-61.

Temple, K.L., and F.W. Delchamps, 1953. Autotrophic bacteria and the

formation of acid in bituminous coals mines. Appl. Microb. 1:

255-258.

179

Veen, H. van, 1977. The behaviour of nitrogen in soil - A simulation

study. Ph.D. thesis. Vrije Univ. Amsterdam, 164 pp.

Wit, C T . de and H. van Keulen, 1972. Transport processes in soils.

Simulation Monographs, Pudoc, Wageningen. 100 pp.

Woldendorp, J.W., 1963. The influence of living plants on denitrifi-

cation. Ph.D.Thesis, Agricultural University, Wageningen, 100 pp.

180

Appendix 6.1 Listing of program on simulation of oxidation and acidifi­

cation processes in acid sulphate soils

DIMENSION AC0ND(21), DFLCA(21), APDIFC(21)

DIMENSION MFLCA(21), DFLH(21), APDIFH(21), MFLH(21)

DIMENSION APDIF(21), DFLS0(21), CAL(21)

DIMENSION MFLS0(21), ADEF(21)

DIMENSION DFLMG(21), APDIFM(21), MFLMG(21), MFLK(21)

DIMENSION MFLAL(21), APDIFA(21), DFLAL(21)

DIMENSION MFLNA(21), APDIFN(21), DFLNA(21)

STORAGE DEF(21), PS04(21), DEFAC(21), RC0X(21), CHYD(21),...

CCA(21), RPHYD(21), RFL0X(21), WC(21)

STORAGE RFLOW(2l), PSI(21), SUCT(21), IPSI(21), C0ND(21),...

COX(21), CS04(21), DEPTH(21), DIFD(21),...

ITC0M(21), WCI(21), AMGK21), AALI(21), AKI(21)

STORAGE APDIFK(21), DFLK(21), CMG(21),...

CK(21), KI(21), CAI(21), MGI(21), HI(21),...

ALI(21), MFL0X(21), DFL0X(21),...

NAI(21) CNA(21), ANAI(21),...

CEC(21), ACAI(21), AHYDK21), TC0M(21), NFLW(21)

*TITLE ACID SULPHATE SOILS

*UNIT M-KG-DAY

INITIAL

NOSORT

* DEFINE INVARIABLE GEOMETRY

TABLE ITCOM(l-2O)=20x.O5

*TABLE FOR EXCHANGED CATIONS EQUIVALENT/M3

TABLE HI(1-20)=20x20.

TABLE MGI(l-20)=20x30.

TABLE KI(l-20)=20x50.

TABLE ALI(l-20)=20x50.

TABLE NAI(l-20)=20x60.

TABLE CAI(l-20)=20x200.

PARAM NC=20

PARAM CHYDI=0.001, CCAI=0.025, CS04I=.l411, C0XI=2.E-4

PARAM CNAI=0.04, CALI=0.0001

181

PARAM CKI=0.050, CMGI=.025

FIXED N5,I,IM,N,N1,N2,N3,N4,NC,II,J,JJ,K,KM,KJ,MM,KK,NP,NS,M

FIXED N6,N7

DO 201 1=1,20

201 TCOM(I)=ITCOM(I)

DIFD(l)=.5xTC0M(l)

DEPTH(l)=.5xTC0M(l)

DO 11 1=2,20

DIFD(I) = (TCOM(I-l)+TCOM(I))x0.5

DEPTH(I) = DEPTH(I-1)+DIFD(I)

11 CONTINUE

DO 999 1=1,NC

IPSI(I)=DPGWT-DEPTH(I)

999 CONTINUE

DO 998 1=1,NC

WCI(I)=AFGEN(PSIT1,IPSI(I)

IF(WCI(I).GE.PVOL)WCI(I)=PVOL

998 CONTINUE

DO 22 I = 1,NC

AMWI(I)=WCI(I)xTCOM(I)

ACAI(I)=AMWI(I)xCCAI

AS04I(I)=AMWI(I)xCS04I

AMOXI(I)=C0XIx(TC0M(I)x(PV0L-WCI(I)))

AHYDI(I)=AMWI(I)xCHYDI

AMGI(I)=AMWI(I)xCMGI

AKI(I)=AMWI(I)xCKI

ANAI(I)=AMWI(I)xCNAI

AALI(I)=AMWI(I)xCALI

CEC(I)=(HI(I)+MGI(I)+KI(I)+NAI(I)+ALI(I)+CAI(I))xTCOM(I)

THYDI(I)=HI(I)xTCOM(I)+AHYDI(I)

TCAI(I)=ACAI(I)+TCOM(I)xCAI(I)

TMGI(I)=AMGI(I)+TCOM(I)xMGI(I)

TKI(I)=AKI(I)+TCOM(I)xKI(I)

TNAI(I)=ANAI(I)+TCOM(I)xNAI(I)

TALI(I)=AAL.I(I)+TCOM(I)xALI(I)

22 CONTINUE

182

PARAM DEVEAP = 0.004,PI = 3.1416

*DAILY EVAPORATION

PARAM WCLIM = 0.25.WCFC =0.39

FUNCTION CONDT1 = (0.059,6.7E-11),(0.177,6.4E-10),...

(0.2,1.7E-9),(0.22,4.5E-9),(0.247,9.5E-9),...

(.255,2.2E-8),(0.277,4.2E-8),(0.308,l.lE-7),...

(0.342,1.75E-7),(0.345,4.04E-7),(0.349.6.04E-7),

(0.35.1.06E-6),...

(0.36,1.59E-6),(0.366,2.81E-6),(0.37,3.36E-6),..

(0.372,3-84E-6),(0.374,4.13E-6),(0.377.4.82E-6),.

(0.38,0.58E-5),(0.383,0.96E-5),(0.385,1.99E-5),..

(0.387,2.55E-5),(0.389,4.18E-5),(0.393,6.87E-5),

(0.395,1.12E-4),(0.398,1.85E-4),(0.4,2.37E-4),..

(0.402,3.04E-4),(0.404,3.89E-4),(0.406,6.53E-4),(0.411,.

8.2E-4),(0.412,1.3E-3),(0.414,1.7E-3),(0.415,2.2E-3),...

(0.416,2.8E-3),(0.421,4.5E-3),(0.429,7.6E-3),...

(0.437,9.2E-3),(0.445,9.8E-3)

FUNCTION SUCT1 = (0.059,10000),(0.177,2000),(0.2,1000),...

(0.22,500),(0.247,200),(0.255,160),(0.277,100),...

(0.308,50),(0.342,25),(0.345,20),(0.349,15),..

(0.355,10),(0.36,7.5),(0.366,5.0),(0.368,4.8),

(0.37,4.4),(0.372,4.),(0.374,3.8),(0.377,3.4),..

(0.38,3.0),(0.383,2.8),(0.385,2.5),(0.387,2.4),

(0.389,2.2),(0.393,2.),(0.395,1.8),(0.398,1.6),.

(0.40,1.5),(0.402,1.4),(0.404,1.3),(0.406,1.2),.

(0.411,1.),(0.412,0.8),(0.414,0.7),..

(0.415,0.6),(0.416,0.5),(0.417,0.4),(0.421,0.311),...

(0.429,0.1),(0.437,0.025),(0.445,0.0)

FUNCTION C0NDT2 = (0.065,1.1E-9),(0.182,1.06E-8),.

(0.203,2.82E-8),(.225,7.44E-8),(0.252,2.7E-7),

(0.257,3.7E-7),(0.283,7.1E-7),(0.318,1.9E-6),.

(0.352,4.9E-6),(0.363,6.7E-6),(0.375,l.E-5),.

(0.392,1.8E-5),(0.405,2.7E-5),(0.42,4.7E-5),..

(0.43,6.9E-5),(0.435,8.1E-5),(0.436,9.6E-5),.

(0.438,l.E-4),(0.44,l.lE-4),(0.443,1.3E-4),..

(0.445,1.5E-4),(0.447,1.7E-4),(0.449.1.9E-4),.

183

(0.452,2.3E-4),(0.457,3.5E-4),(0.46,3.9E-4),...

(0.463,4.4E-4),(0.466,6.lE-4),(0.468,7.3E-4),...

(0.471,9.E-4),(0.474,1.2E-3),(0.477,1.9E-3),...

(0.482,2.9E-3),(0.492,8.E-3),(0.5,1.15E-2),...

(0.507.1.3E-2)

FUNCTION SUCT2 = (0.065,10000),(0.182,2000) ,.. .

(0.203,1000),(0.225,500),(O.252,200),(O.257,160),...

(0.283,100),(0.318,50),(0.352,25),(0.363,20),...

(0.375,15),(0.392,10),(0.405,7.5),(0.42,5.),...

(0.43,3.8),(0.435,3.4),(0.436,3.),(0.438,2.8),...

(0.44,2.6),(0.443,2.4),(0.445,2.2),(0.447,2.),...

(0.449,1.8),(0.452,1.6),(0.455,1.4),(0.457,1.2),...

(0.46,1.1),(0.463,1.),(0.464,0.9),(.466,0.8),...

(0.471,0.6),(0.474,0.5),(0.477,0.4),(0.482,0.31),...

(0.492,0.1),(0.5,0.025),(0.504,0.0)

FUNCTION PSIT1 = -30.,1.5,0.,0.445,0.025,0.437,0.1,0.429,...

0.31,0.421,0.4,0.417,0.5,0.416,0.6,0.415,0.7,0.414,...

0.8,0.412,1.,0.411,1.2,0.406,1.3,0.404,1.4,0.402,...

1.5,0.4,1.6,.398,1.8,.395,2.,.393,2.2,.389,...

2.4,.387,2.8,.383,3.,.38

FUNCTION PSIT2 = -30.,1.5,0.,.504,.025,0.5,0.1,.492,0.31,.482, .4,.

.477,.5,.474,.6,.471,.8,.466,.9,.464,1.,.463,1.1,.46,...

1.2,.457,1.4,.455,1.6,.452,1.8,.449,2.,.447,...

2.2,.445,2.4,.443,2.6,.44,3.8,.43

PARAM DWC=1.

*MOISTURE CONTENT TO BE REMOVED BEFORE GW SHIFTS

PARAM PVOL = 0.445

*TOTAL PORE VOLUME IN M3/M3

DYNAMIC

NOSORT

CONSAT = AFGEN(CONDTl,PVOL)

DO 59 I = 1,NC

WC(I) = AMW(I)/TCOM(I)

IF(WC(I).GE.PVOL)WC(I)=PVOL

CS04(I) = AS04(I)/AMW(I)

DO 55 J = 1,NC

184

IM = J

IF(WC(J).GE.PVOL) GO TO 54

COX(J) = AMOX(J)/(ITCOM(J)x(PVOL-WC(J)))

55 CONTINUE

GO TO 53

54 CONTINUE

DO 52 K = IM,NC

COX(K) = 0

52 CONTINUE

53 CONTINUE

59 CONTINUE

N=(DPGWT/0.04999)+l.

IF(N.LT.5)STOP

IPSI(N-1)=DPGWT-DEPTH(N-1)

IF(N.GT.21)STOP

WC(N-1)=AFGEN(PSIT1,IPSI(N-1))

WC(N)=PVOL

*DEFINITION OF MOISTURE FLOW, UNSATURATED

*DOWNWARD FLOW IS POSITIVE

DO 58 I = 1,NC

COND(I) = AFGEN(CONDTl,WC(I))

SUCT(I) = AFGEN(SUCT1,WC(I))

58 CONTINUE

ACOND(l) = COND(l)

PSI(l) = -SUCT(1)+DPGWT-DEPTH(1)

DO 57 I = 2,NC

ACOND(I) = (COND(I-l)+COND(I))x0.5

PSI(I) = -SUCT(I)+DPGWT-DEPTH(I)

57 CONTINUE

FUNCTION REDFDT = -1.5,0.0.,.075,.05,.1,.1,.2,.2,.375,.3,

.5,.4,.725,.5,.775,.75,.9,l.,l.,1.1,1.,2.,1.

WCPR = (WC(1)-WCLIM)/(WCFC-WCLIM)

IF(WCPR.LT.O.)WCPR=0

REDFD = AFGEN(REDFDT,WCPR)

AMP=DEVAPxPI

EVAPO = AMXl(0.0001,AMPx(SIN(2.xPIxTIME)))xREDFD

185

RFLOW(l) = -EVAPO

*GROUNDWATER TABLE

INCON DPGWT = .30

N = (DPGWT/0.04999)+l.

J=N

JJ=NC+1

DO 97 I = J,JJ

REFLOW(I) = RFLOW(I-l)

97 CONTINUE

KM = N-l

DO 95 I = 2,KM

RFLOW(I) = ACOND(I)x(PSI(I-l)-PSI(I))/DIFD(I)

IF(ABS(RFLOW(I)).LT.0.01xDELT)RFLOW(I)=0.0

95 CONTINUE

AMW = INTGRL(AMWI,RNFLW,20)

DO 96 I = 1,NC

NFLW(I) = RFLOW(I)-RFLOW(I+l)

96 CONTINUE

SORT

PROCEDURE RNFLW,DELWl,DELW,RFLOW,TCOM,DELXX,PSI = ALGBR(DPGWT,.

SUCT,NFLW,DELX)

IF(DPGWT.LT.1.)DELW=0.0

IF(DPGWT.GE.1.)GO TO 121

DO 101 1=1,NC

DELW=DELW+NFLW(I)xDELT

101 CONTINUE

IF(ABS(DELW).GT.0.004xDELT) GO TO 102

GO TO 109

102 DPGWT = DPGWT-DELWx0.2

IF(DPGWT.GE.1.)DPGWT=1.

121 N=(DPGWT/0.04999)+l.

IF(N.LT.5)STOP

ETCOM=TCOM(N-l)

EWC=WC(N-1)

TCOM(N-2)=ITCOM(N-2)

DEPTH(N-2)=DEPTH(N-3)+0.5x(TCOM(N-2)+TCOM(N-3))

186

104 TCOM(N-l)=DPGWT-DEPTH(N-2)-0.5xTCOM(N-2)

DEPTH(N-l)=DEPTH(N-2)+0.5x(TCOM(N-2)+TCOM(N-l)

Nl=N-4

N5=N-3

N6=N-5

N2=N-1

N7=N2-1

DO 133 I=N1,N7

AMW(I)=AMW(I)

WC(I)=WC(I)

133 CONTINUE

PSI(N1-1)=-SUCT(N1-1)+DPGWT-DEPTH(N1-1)

IPSI(N-1)=DPGWT-DEPTH(N-1)

WC(N-1)=AFGEN(PSIT1,IPSI(N-1))

DO 132 I=N1,N2

SUCT(I)=AFGEN(SUCT1,WC(I))

COND(I)=AFGEN(CONDT1,WC(I))

ACOND(I)=(COND(I)+COND(I-l))x0.5

132 CONTINUE

DO 106 I=N1,N2

DIFD(I)(TCOM(I)+TCOM(I-l))x0.5

PSI(I)=-SUCT(I)+DPGWT-DEPTH(I)

106 CONTINUE

DO 114 I=N1,N2

RFLOW(I)=ACOND(I)x(PSI(I-l)-PSI(I))/DIFD(I)

IF(ABS(RFLOW(I)).LT.0.01xDELT)RFLOW(I)=0.0

114 CONTINUE

IF(N.EQ.21) GO TO 111

111 N3=NC+1

DO 115 I=N,N3

RFLOW(I)=RFLOW(I-l)

115 CONTINUE

DO 107 I=N1,N

NFLW(I)=RFL0W(I)-RFL0W(I+1)

107 CONTINUE

IF(N.FQ.21) GO TO 109

187

DELX=0.O

DO 108 I=N1,N

DELX=DELX+NFLW(I)xDELT

108 CONTINUE

DELXX=DELX+(WC(N-l)-EWC)xETCOM+(WC(N-l)-...

PVOL)x(TCOM(N-l)-ETCOM)

DELW1=DELW

DELW=DELW-DELXX

IF(ABS(DELXX).GT.ABS(DFLW1)) GO TO 109

IF(ABS(DELW).LT.0.002xDELT) GO TO 109

DO 131 I=N1,N7

AMW(I)=AMW(I)+NFLW(I)xDELT

WC(I)=AMW(I)/TCOM(I)

131 CONTINUE

GO TO 102

109 CONTINUE

DO 110 1=1,NC

RNFLW(I)=NFLW(I)

110 CONTINUE

ENDPRO

*MOVEMENT OF SULPHATE

NOSORT

DO 89 1=2,NC

MFLSO(I) = RFL0W(I)x.5x(CS04(I)+CS04(I-l))

APDIF(I) = DNOTxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLSO(I) = APDIF(I)x(CS04(I-l)-CS04(I))

89 CONTINUE

PARAM DNOT = 6.5E-5.T0RT = .7.DISP = .03

MFLSO(l) = RFLOW(l)xCS04(l)

APDIF(l) = DNOTxWC(l)xTORT/DIFD(l)+ABS(REFLOW(l))xDISP

DFLSO(l) = 0.0

DO 86 I=N,N3

MFLSO(I) = MFLSO(I-l)

DFLSO(I) = DFLSO(I-l)

86 CONTINUE

AS04=INTGRL(AS04I,NFS04,20)

188

DO 79 1=1,NC

DEFAC(I) = AFGEN(DEFACT,(PVOL-WC(I)))

DEF(I) = DEFAC(I)xDZERO

79 CONTINUE

IF(N.LE.NC) GO TO 71

IF(N.GT.NC)N=NC

GO TO 71

71 DO 78 1=2,KM

ADEF(I) = (DEF(I)+DEF(I-l))x.5

DFLOX(I)=ADEF(I)x(COX(I-l)-COX(I))/DIFD(I)

78 CONTINUE

DFLOX(l) = DEF(l)x(COUT-COX(l))/DIFD(l)

KK = N-l

KJ=N-2

DO 77 I=N,JJ

DFLOX(I) =0.0

MFLOX(I) =0.0

77 CONTINUE

DO 72 1=1,KK

RFLOX(I) = DFLOX(I)+MFLOX(I)

72 CONTINUE

DO 76 1=1,KJ

MFLOX(I)=RNFLW(I)xCOX(I)

78 CONTINUE

MFLOX(N-1)=RFLOW(N-1)xCOX(N-1)

DO 74 I=N,JJ

MFLOX(I)=RNFLW(I)xCOX(I)

74 CONTINUE

*PRODUCTION OF SULPHATE

FUNCTION DEFACT = 0.00,0.00001,.01,.00005,.10,.002,.13,.0343,.

.139,-0441,...

.16,.0669,.168,.0781,.176,.089,.184,.0975,.20,.1165,...

.211,. 1206,.216,.122,.227,.1234,.245,.1242,...

.329,.1316,.395,.144,.460,.1579,.531,.167

PARAM PYRL = 0.3

NP=(PYRL/0.04999)+!.

189

N4=NP-1

IF(N.GT.NP) GO TO 84

PS04(N)=0.0

RCOX(N)=0.0

GO TO 87

84 NS=N-1

DO 83 I=NP,NS

IF(RFLOX(I).LE.0.0)FX=0.0

IF(RFLOX(I).GT.O.0)FX=1.0

PS04(I)=FXxO.4xRFL0X(I)x1.6

RCOX(I)=FXxO.4.RFLOX(I)

83 CONTINUE

87 DO 81 1=1,N4

PS04(I)=0.0

RCOX(I)=0.0

81 CONTINUE

DO 85 I=N,JJ

PS04(I)=0.0

RCOX(I)=0.0

85 CONTINUE

DO 70 1=1,NC

NFL0X(I)=DFL0X(I)-DFL0X(I+1)-MFL0X(I)-RC0X(I)

70 CONTINUE

DO 88 1=1,N7

NFS04(I)=MFLS0(I)-MFLS0(I+1)+DFLS0(I)-DFLS0(I+1)+PS0(I)

88 CONTINUE

NFS04(N6)=-RFLOW(N6)x(CS04(N6)-CS04(N6+l))+...

DFLSO(N6)-DFLSO(N6+1)+PS04(N6)

NFS04(Nl)=-RFL0W(Nl+l)x(CS04(Nl)-CS04(Nl+l))+...

DFLSO(NI)-DFLSO(Nl+1)+PS04(NI)

DO 880 I=N5,NC

NFS04(I)=MFLS0(I)-MFLS0(I+1)+DEFLS0(I)-DFLS0(I+1)+PS04(1)

880 CONTINUE

AMOX = INTGRI (AMOXI,NFLOX,20)

PARAM DZERO = 2.26E-5.C0UT = 2.75E-4

PARAM TAK=+1.0

190

PARAM EPS=0.000001

PARAM A1PH2=0.2,BETA2=0.4,CD=0.25

* H/K CA/MG KD1/KMI

PARAM ALPH3=0.5,SIGMA=0.37

* H/NA NA/AL

FIXED IER.IK.IEPS

* ACIDITY OF SOIL COMPARTMENTS

PARAM DNOTH = 3.0E-4,DNOTCA = 1.03E-4

PARAM DN0TAL=1.5E-4,DN0TNA=1.3E-4

PARAM DNOTMG=0.61E-4,DNOTK=1.64E-4

DO 69 1=1,NC

RPHYD(I) = PSO4(I)x0.0208

69 CONTINUE

DO 68 1=1,NC

TM3 = AHYD(I)/ITCOM(I)

TM1=ANA(I)/ITC0M(I)

TD1 = ACA(I)/ITCOM(I)

TM2=AK(I)/ITC0M(I)

TD2=AMG(I)/ITCOM(I)

TT1=AAL(I)/ITC0M(I)

CECE=CEC(I)

XST=TM1/10

IF(TAK.LT.O.)XST=CNA(I)

IF(XST.LT.1.F-20)XST=TD1/10

Z,IER,IK,IEPS=RINI(FF,DERF,XST,EPS,20,IM1,IM2,IDO,CD,TD2,.

CECE,ALPH2,BETA2,IM3,TT1,SIGMA,ALPH3)

CALCULATION OF RESULTING CONCENTRATIONS

X1=Z

Yl=CDxZxZ

X2=ALPH2xZ

X3=ALPH3xZ

Y2=BETA2xYl

Y3=SIGMAxZxZxZ

CHYSOL=X3xTM3/(1.+X3)

CHYD(I)=CHYSOL

CALSOL=Y3xTT1/C1.+Y3)

191

CAL(I)=CALSOL/WC(I)

ALI(I)=TT1-CALS0L

CNASOL=XlxTMl/(l.+Xl)

CNA(I)=CNASOL/WC(I)

NAI(I)=TM1-CNAS0L

CKS0L=X2xTM2/(1.+X2)

CK(I)=CKSOL/WC(I)

KI(I)=TM2-CKS0L

CCASOL=YlxTDl/(l.+Yl)

CCA(I)=CCASOL/WC(I)

CAI(I)=TD1-CCAS0L

CMGS0L=Y2xTD2/(1.+Y2)

CMG(I)=CMGSOL/WC(I)

MGI(I)=TD2-CMGS0L

68 CONTINUE

*BOUNDARY CONDITION

DFLAL(1)=0.0

DFLNA(1)=0.0

DFLH(1)=0.0

DFLCA(1)=0.0

DFLMG(1)=0.0

DFLK(1)=0.0

CAL(21)=CAL(20)

CNA(21)=CNA(20)

CHYD(21)=CHYD(20)

CCA(21)=CCA(20)

CMG(21)=CMG(20)

CK(21)=CK(20)

MFLH(l)=RFLOW(l)xCHYD(l)

MFLCA(1)=RFLOW(1)xCCA(1)

MFLNA(1)=RFLOW(1)xCNA(1)

MFLAL(l)=RFLOW(l)xCAL(l)

MFLMG(l)=RFLOW(l)xCMG(l)

MFLK(l)=RFLOW(l)xCK(l)

DO 67 1=2,NC

MFLH(I) = RFLOW(I)x.5x(CHYD(I)+CHYD(I-l))

192

APDIFH(I) = DNOTHxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLH(I) = APDIFH(I)x(CHYD(I-l)-CHYD(I))

MFLCA(I) = RFL0W(I)x0.5x(CCA(I)+CCA(I-l))

APDIFC(I) = DNOTCAxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLCA(I) = APDIFC(I)x(CCA(I-l)-CCA(I))

MFLMG(I)=RFLOW(I)x0.5x(CMG(I)+CMG(I-l))

APDIFM(I)=DNOTMGxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLMG(I)=APDIFm(I)x(CMG(I-l)-CMG(I))

MFLK(I)=RFLOW(I)x0.5x(CK(I)+CK(I-l))

APDIFK(I)=DNOTKxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLK(I)=APDIFK(I)x(CK(I-l)-CK(I))

MFLAL(I)=REFLOW(I)x0.5x(CAL(I)+CAL(I-l))

APDIFA(I)=DNOTALxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLAL(I)=APDIFA(I)x(CAL(I-l)-CAL(I))

MFLNA(I)=RFLOW(I)x0.5x(CNA(I)+CNA(I-l))

APDIFN(I)=DNOTNAxWC(I)xTORT/DIFD(I)+ABS(RFLOW(I))xDISP

DFLNA(I)=APDIFN(I)x(CNA(I-l)-CNA(I))

67 CONTINUE

DO 61 I=N,N3

MFLAL(I)=MFLAL(I-1)

DFLAL(I)=DFLAL(I-1)

MFLNA(I)=MFLNA(I-1)

DFLNA(I)=DFLNA(I-1)

MFLH(I) =MFLH(I-1)

DFLH(I) =DFLH(I-1)

MFLCA(I)=MFLCA(I-1)

DFLCA(I)=DFLCA(I-1)

MFLK(I)=DFLK(I-1)

MFLMG(I)=MFLMG(I-1)

DFLMG(I)=DFLMG(I-1)

61 CONTINUE

DO 66 1=1,N7

NFLHYD(I)=MFLH(I)-MFLH(I+1)+DFLH(I)-DFLH(I+1)+RPHYD(I)

NFLCA(I)=MFLCA(I)-MFLCA(I+1)+DFLCA(I)-DFLCA(I+1)

NFLMG(I)=MFLMG(I)-MFLMG(I+1)+DFLMG(I)-DFLMG(I+1)

NFLK(I)=MFLK(I)-MFLK(I+1)+DFLK(I)-DFLK(I+1)

193

NFLAL(I)=MFLAL(I)-MFLAL(I+1)+DFLAL(I)-DFLAL(I+1)

NFLNA(I)=MFLNA(I)-MFLNA(I+1)+DFLNA(I)-DFLNA(I+1)

66 CONTINUE

NFLHYD(N6)=-RFLOW(N6)x(CHYD(N6)-CHYD(N6+l))+...

DFLH(N6)-DFLH(N6+1)+RPHYD(N6)

NFLHYD(Nl)=-RFLOW(Nl+l)x(CHYD(Nl)-CHYD(Nl+l))+...

DFLH(N1)-DFLH(N1+1)+RPHYD(N1)

NFLCA(N6)=-RFLOW(N6)x(CCA(N6)-CCA(N6+l))+...

DFLCA(N6)-DFLCA(N6+1)

NFLCA(Nl)=-RFLOW(Nl+l)x(CCA(Nl)-CCA(Nl+l))+...

DFLCA(Nl)-DFLCA(Nl+1)

NFLMG(Nl)=-RFLOW(Nl+l)x(CMG(Nl)-CMG(Nl+l))+...

DFLMG(N1)-DFLMG(N1+1)

NFLMG(N6)=-RFLOW(N6)x(CMG(N6)-CMG(N6+l)+...

DFLMG(N6)-DFLMG(N6+1)

NFLK(N6)=-RFLOW(N6)x(CK(N6)-CK(N6+l))+DFLK(N6)-DFLK(N6+l)

NFLK(Nl)=-RFLOW(Nl+l)x(CK(Nl)-CK(Nl+l)+...

DFLK(N1)-DFLK(N1+1)

NFLAL(N6)=-RFLOW(6)x(CAL(N6)-CAL(N6+l)+...

DFLAL(N6)-DFLAL(N6+1)

NFLAL(Nl)=-RFLOW(Nl+l)x(CAL(Nl)-CAL(Nl+l))+...

DFLAL(Nl)-DFLAL(Nl+1)

NFLNA(N6)=-RFLOW(N6)x(CNA(N6)-CNA(N6+l))+...

DFLNA(N6)-DFLNA(N6+1)

NFLNA(Nl)=-RFLOW(N+l)x(CNA(Nl)-CNA(Nl+l)+...

DFLNA(N1)-DFLNA(N1+1)

DO 669 I=N5,NC

NFLHYD(I)=MFLH(I)-MFLH(I+1)+DFLH(I)-DFLH(I+1)+RPHYD(I)

NFLCA(I)=MFLCA(I)-MFLCA(I+1)+DFLCA(I)-DFLCA(I+1)

NFLMG(I)=MFLMG(I)-MFLMG(I+1)+DFLMG(I)-DFLMG(I+1)

NFLK(I)=MFLK(I)-MFLK(I+1)+DFLK(I)-DFLK(I+1)

NFLAL(I)=MFLAL(I)-MFLAL(I+1)+DFLAL(I)-DFLAL(I+1)

NFLNA(I)=MFLNA(I)-MFLNA(I+1)+DFLNA(I)-DFLNA(I+1)

669 CONTINUE

AHYD = INTGR(THYDI,NFLHYD,20)

AAL=INTGRL(TALI,NFLAL,20)

194

ANA=INTGRL(TNAI,NFLNA,20)

ACA=INTGRL(TCAI,NFLCA,20)

AMG=INTGRL(IMGI,NFLMG,20)

AK=INTGRL(TKI,NFLK,20)

TEVAPO=INTGRL(0.,EVAPO)

TIMER FINTIM = 30.,OUTDEL=l.,PRDEL=1.,DELT=0.001

METHOD RECT

PRINT CHYD(1-20),COX(1-20),...

DPGWT,TEVAPO,DELW,DELXX

OUTPUT WC(l-20), NFLOX(1-20)

OUTPUT RFL0W(l-20),PS04(l-20)

NOSORT

IF(KEEP.EQ.O) GO TO 700

IF(IMPULS(0.,PRDEL).LT.0.5) GO TO 700

700 CONTINUE

SORT

NOSORT

END

STOP

SUBROUTINE CAT(Z,FF,DERF,TM1,TM2,TD1,CD;TD2,CEC,ALPH2,BETA2,

1TM3.TT1.SIGMA,ALPH3)

* SUBROUTINE CAT FOR CALCULATION OF CATION EXCHANGE EQUATION AND

DERIVATIVE

* Z-RESULTANT ROOT OF EQUATION F(Z)

* FF RESULTANT FUNCTION ROOT OF EQUATION F(Z)

* DERF RESULTANT VALUE OF DERIVATIVE AT ROOT Z

* TM1-TOTAL AMOUNT MONOVALENT CATION1 SODIUM

* TM2-TOTAL MONOVALENT CATI0N2 POTASSIUM

* TM3- TOTAL MONOVALENT CATION3 HYDROGEN

* TD1 TOTAL AMOUNT OF DIVALENT CATION1 CA

* TD2 TOTAL DIVALENT CATION2 MG

* TT1- TOTAL TRIVALENT CATION1 ALUMINIUM

* CEC = SUM AM(I)+AD(I)+AT(I)

* CD=KD1/KM1

* ALPH2=KM1/KM2

195

* ALPH3=KM1/KM3

* BETA2=KD1/KD2

* SIGMA=KT1/KD1

* C JL.

F1=TM1/(1.+Z)

F2=TM2/Cl.+ALPH2xZ)

F3=TM3/(1.+ALPH3xZ)

F4=TDl/(l.+CDxZxZ)

F5=TD2/C1.+BETA2xCDxZxZ)

F6=TT 1 / ( 1. +SI GMAxZxZxZ )

FF=F1+F2+F3+F4+F5+F6-CEC

DERF1=TM1/(1.+Z)xx2

DERF2=ALPH2xTM2/(1.+ALPH2xZ)xx2

DERF3=ALPH3xTM3/(1.+ALPH3xZ)xx2

DERF4=TDlxCDxZx2./(1.+CDxZxZ)xx2

DERF5=TD2xCDxZx2.xBETA2/(1.+CDxZxZxBETA2)xx2

DERF6=3xZxZxTTlxSIGMA/(l.+SIGMAxZxZxZ)xx2

DERF=-1.x(DERF1+DERF2+DERF3+DERF4+DERF5+DERF6)

RETURN

END

* RTNI SUBROUTINE.NEWTON ITERATION METHOD

*

SUBROUTINE RTNI(FF,DERF,XST,EPS,LEND,TM1,TM2,ID1,CD,TD2,

1 CEC,ALPH2,BETA2,TM3,TT1,SIGMA,ALPH3,X,1ER,IK,IEPS)

*

*

* X- RESULTANT ROOT OF EQUATION F(X)=0

* FF- RESULTANT FUNCTION VALUE AT ROOT X

* DERF- RESULTANT VALUE OF DERIVATIVE AT ROOT X

* XST -INITIAL VALUE OF X FOR ITERATION

* FPS- UPPERBOUND OF ERROR OF RESULT X

* IEND- MAXIMUM NUMBER OF ITERATION STEP SPECIFIED

196

* IER=0-NO ERROR

* IER=l-NO CONVERGENCE AFTER IEND STEP

* IER=2-DERF EQUAL TO ZERO AT SOME ITERATION STEPS

* IER=3-AT SOME PLACE DX.GT.X WAS CORRECTED, MESSAGE ONLY

* IER=4-AFTER CORRECTION DX RESTS.GT.X

* IK-ITERATION COUNTER

* PREPARATION ITERATION

IEPS=0

21 IK=0

IER=0

X=XST

TDL=X

CALL CAT(T0L,FF,DERF,TM1,TM2,ID1,CD,TD2,CEC,ALPH2,BETA2,

1TM3,TT1,SIGMA,ALPH3)

13 TOLF=100.*EPS

* START ITERATION LOOP •A.

6 IK=IK+1

IF(FF)1,7,1

* EQUATION IS NOT SATISFIED BY X

1 IF(DERF)2,8,2

* ITERATION IS POSSIBLE

2 DX=FF/DERF

* CHECK FOR NEGATIVE X

14 IF(DX-X)17,15,15

15 DX=0.9xDX

IF(IK-20)16,18,18

* IER=3- AT SOME PLACE DX.GT.X WAS CORRECTED****«^****

16 IER=3

GO TO 14

17 CONTINUE

X=X-DX

197

TOL=X

CALL,CAT(T0L,FF,DERF,TM1,TM2.TD1,CD,TD2,CEC,ALPH2,BETA2,

1TM3.TT1,SIGMA,ALPH3)

CONTINUE JU

* TEST ON SATISFACTORY ACCURACY*******

10 TOL=EPS

A=ABS(X)

IF(A-1.)4,4,3

3 TOL=TOL*A

4 IF(ABS(DX)-TOL)5,5,36

5 IF(ABS(FF)-TOLF)7,7,36

36 IF(IK-IEND)6,6,26

* END OF ITERATION LOOP

*

* NO CONVERGENCE AFTER IEND STEPS

26 IER=1

IF(IEPS-2)19,7,7

*

* EPS IS INCREASED BY FACTOR TEN

19 IEPS=IEPS+1

EPS=EPSxlO.

* BACK TO ITERATION CYCLE WITH NEW EPS

TOLF = lOO.xEPS

GO TO 10

7 RETURN

* ERROR RETURN IN CASE OF ZERO DIVISION

8 IER=2

RETURN

* C

* ERROR RETURN FOR DX.GT.X,CORRECTION NOT EFFECTIVE

18 IER=4

RETURN

END

198

Appendix 6.2 List of acronyms used in the program

Acronym Definition Units

AALI

ACAI

ACOND

AHYDI

AKI

ALI

AMGI

AMOX

AMOXI

AMW

AMWI

ANAI

APDIFA

APDIFC

APDIFH

APDIFK

APDIFM

APDIFN

CAI

CALI

CCAI

CEC

CHYDI

CKI

CMGI

CNAI

initial amount of aluminium

initial amount of calcium

average conductivity

initial amount of hydrogen

initial amount of potassium

initial exchangeable aluminium

initial amount of magnesium

amount of oxygen

initial amount of oxygen

amount of water

initial amount of water

initial amount of sodium

apparent diffusion coefficient of aluminium

apparent diffusion coefficient of calcium

apparent diffusion coefficient of hydrogen

apparent diffusion coefficient of potassium

apparent diffusion coefficient of magnesium

apparent diffusion coefficient of sodium

initial exchangeable calcium

initial concentration of aluminium in

soil solution

initial concentration of calcium in

soil solution

cation exchange capacity

initial concentration of hydrogen in

soil solution

initial concentration of potassium in

soil solution

initial concentration of magnesium in

soil solution

initial concentration of sodium in

soil solution

(eq)

(eq)

(m.d"

(eq)

(eq)

(eq.m

(eq)

(kg)

(kg)

(m3)

(m3)

(eq)

(m.d.

(m.d"

(m.d"

(m.d"

(m.d"

(m.d"

(eq.m

a)

"3)

- 1 ) l) l) l)

')

"3)

(eq.m )

(eq.m )

(eq.m )

(eq.m )

(eq.m )

(eq.m )

(eq.m )

199

Acronym Definition Units

COND hydraulic conductivity

CONSAT saturated hydraulic conductivity

COX concentration of oxygen

COXI initial concentration of oxygen

CSO, concentration of sulphate

CSO.I initial sulphate concentration

DEF effective diffusion coefficient

DEFAC diffusion efficiency factor

DEPTH distance from the middle of a compartment

to the soil surface

DEVAP evaporation rate from soil surface

DFLAL rate of diffusion of aluminium

DFLCA rate of diffusion of calcium

DFLH rate of diffusion of hydrogen

DFLK rate of diffusion of potassium

DFLMG rate of diffusion of magnesium

DFLNA rate of diffusion of sodium

DFLOX rate of oxygen diffusion

DFLSO rate of diffusion of sulphate

DIFD distance between the centres of two

adjacent compartments

DISP dispersion factor

DNOTH diffusion coefficient of hydrogen

DNOTAL diffusion coefficient of aluminium

DNOTCA diffusion coefficient of calcium

DNOTK diffusion coefficient of potassium

DNOTMG diffusion coefficient of magnesium

DNOTNA diffusion coefficient of sodium

DPGWT depth of groundwater table

DZERO diffusion coefficient of oxygen in air

HI initial exchangeable hydrogen

IPSI initial hydraulic potential

ITCOM initial thickness of compartment

(m.d"1)

(m.d"1)

(kg.m )

(kg.m ) i "3-, (eq.m ) t -3-» (eq.m )

(m .d )

(unitless)

(m) 1,

(m.d *) i - 2 A-(eq.m .d

i "2 A-] (eq.m .d t "2 A-] (eq.m .d t "2 j - 1 (eq.m .d

(eq.m .d

(eq.m .d

(kg.m .d f - 2 , , - ] (eq.m .d

l) L) L) l) )

[) L) )

(«0

(m)

(m2.d~

(m2.d~

(m2.d"

(m2.d"

(m2.d"

(m2.d"

(m)

(m2.d_1)

(eq.m )

(m)

(m)

200

Acronym Definition Units

KI initial exchangeable potassium

MFLAC rate of mass flow of calcium

MFLAL rate of mass flow of aluminium

MFLH rate of mass flow of hydrogen

MFLK rate of mass flow of potassium

MFLMG rate of mass flow of magnesium

MFLNA rate of mass flow of sodium

MFLOX rate of oxygen mass flow

MFLSO rate of mass flow of sulphate

MGI initial exchangeable magnesium

NAI initial exchangeable sodium

NFLAL net flow rate of aluminium

NFLCA net flow rate of calcium

NFLHYD net flow rate of hydrogen

NELK net flow rate of potassium

NFLMG net flow rate of magnesium

NFLNA net flow rate of sodium

NFLOX net flow rate of oxygen

NFLSO net flow rate of sulphate

NFLW net flow rate of water

PS1 hydraulic potential

PSO, rate of sulphate production

PVOL pore volume

PYR depth of pyritic layer

RCOX rate of oxygen consumption

REDFDT reduction factor for actual evaporation

RFLOW flow rate of water

RHYD rate of production of hydrogen

SUCT matric suction

TALI total amount of aluminium

TCAI total amount of calcium

TCOM thickness of compartment

TD total divalent cations

eq .

eq .

eq

eq .

eq .

eq

eq

kg.

eq

> q

eq

eq .

eq .

eq .

eq .

eq .

eq .

kg-

eq .

- J , m , - ? m

- 2 m

- ? m

- ? m

- ? m

- ? m

- 2 m

- ? m

- 3 , m , m ,

- ? m

- ? m

- 9 m

- ? m

- ? m

- ? m

- 2 m

- ? m

m.d" 1)

m)

kg .

d

d'

d

d

d

d

d'

d

d

d

d

d

d

d

d"

d

- 3 d - ] m

3 - 3 . mm )

m) -:

m uni

m.d

eq .

m)

eq)

eq)

m)

eq)

1 , )

') 1 , )

1 , )

1 , )

1 , )

X) 1 , )

1 , )

1 , )

1 , )

1 , )

1 , )

1 , )

) 1 , )

)

.m .d )

t l e s s ]

- 1 ) - ? - 1

m d )

201

Acronym Definition Units

THYDI total amount of hydrogen

TK1 total amount of potassium

TM total monovalent cations

TMGI total amount of magnesium

TNAI total amount of sodium

TT total trivalent cations

WC water content

WCFC water content at field capacity

WCI initial water content

WCLIM water content at wilting point

(eq)

(eq)

(eq)

(eq)

(eq)

(eq) ( 3 -Cm m i 3 -(m m i 3 -(m m r 3 -(m m

3) 3) 3) 3 )

202

SUMMARY

In potential acid sulphate soils acidity may arise from any combination

of reclamation and drainage lowering the groundwater table in adjacent

areas, and unusually dry seasons affecting the regional groundwater

table. In the long run, natural processes of deacidification will fi­

nally make these soils productive. But this natural process is very

slow and may take decades for any significant improvement. Thus natural

reclamation does not provide the solution to the immediate need of in­

creasing food production at a sufficiently high rate. Developing eco­

nomic means of enhancing the process of reclamation of these soils is

therefore considered very important. Feasible management packages for

the development of acid sulphate soils are determined by the soils, the

climate, the hydrology and the economic opportunities.

The causes of low productivity of acid sulphate soils include soil

acidity, salinity, aluminium toxicity, iron toxicity and low nutrient

status. Different reclamation and improvement methods for low land rice

are reviewed in Chapter 2. A simple low-cost lysimeter drum (60 cm

diameter, 90 cm depth) was developed to collect undisturbed soil cores

for studying the chemical changes and the growth of rice in acid sul­

phate soils. Forty undisturbed soil cores from Aparri and Sinacaban

soils in the Philippines were subjected to different water management

practices, liming rates and mulch application for two leaching periods

and three rice crops. There was a great difference in chemical proper­

ties and grain yields of the two soils. In Aparri soil, there was no

marked effect of drainage, liming and mulch practices on the chemical

properties of the soil solution during the two leaching periods and

203

during three rice crops. Also the grain yields of three crops in this

soil were not influenced by different treatments.

In Sinacaban soil, the effects of drainage, liming and agronomic prac­

tices on chemical properties of soil solutions were very pronounced.

Deep drainage of the soil created favourable conditions for pyrite 2+ 3+

oxidation which resulted in high acidity and high Fe and Al . Shal­low drainage did not cause severe oxidation in the subsoil layers and

2+ 3+ produced less acidity and Fe , Al . Shallow drainage in combination

with mulch application (5 cm of rice straw) minimized the water loss

from the soil, and hindered oxygen movement to the subsoil. This re-2+ 3+

sulted in less acidity development and less Fe , Al . When the soil 2+

was continuously submerged, there was no pyrite oxidation, and no Fe 3+

and Al production.

The influence of different treatments on grain yields was very pro­

nounced. Deep drainage treatments gave the poorest yield in both the

second and third crops. Highest yields were obtained in the surface

flushing treatments, the next highest yields with shallow drainage.

Mulching increased grain yield by 67 and 30 percent for the second and

third crops respectively. In deep drainage treatments, only high

amounts of lime, 2.5 tons/ha produced a yield exceeding the equivalent

of about 1 ton/ha. In this chapter, the concept of average mineral

stress index (AMSI) was introduced to correlate grain yield and toxic

elements in acid sulphate soils (pH, AI, Fe).

During the dry season, oxidation and acidification occur when ground­

water falls below the sulphic layers in the subsoil.

In Chapter 3, a study on the evaporation and acidification process in

an acid sulphate soil was carried out in forteen undisturbed soil col­

umns of 20 cm in diameter and 70 cm length from an acid sulphate soil

in Mijdrecht, the Netherlands. These columns were subjected to two

groundwater levels: 40 cm and 65 cm below the soil surface, 5 different

durations of evaporation and 2 agronomic practices. The average total

acidity over 14 layers in the profile did not show much variation among

treatments. The presence of a peat layer on the surface reduced the

rate of acidification, presumably mainly by reducing. The evaporation

rate and perhaps by hampering the oxygen movement in the profile. In

treatments with low groundwater table, the average pH decreased sharply

204

at increasing evaporation.

When acid sulphate soils develop, dramatic changes in the chemistry of

surface waters take place and these are exported from the reclaimed

area as drainage waters. Acid sulphate floodwaters generated over large

areas of acid sulphate soils may adversely affect crops growing on ad­

jacent, better soils.

In Chapter 4, a study on the one-time and cumulative effects of acid

sulphate floodwater on the growth of rice and on the chemical changes

in three acid sulphate soils were investigated in two successive pot

experiments. Artificial acid floodwater were made with pH ranges from

3.5 to 5.8, Al from 0 to 300 mg/1 and Fe + from 0 to 500 mg/1.

In both experiments, pH of acid floodwater alone, as low as 3.5, did

not affect the chemical changes of three acid sulphate soils, whereas

cid 2+

3+ 2+ the presence of Al and Fe in acid sulphate floodwater produced low

2 pH and enhanced the solubility of Fe

pH of acid sulphate floodwater alone as low as 3.5 showed no effect of

the growth of rice at on early stage of growth. Dry matter yields were 2+ 3+

negatively correlated with the applied Fe and Al + 3+ 2+

A single factor, total acidity, being the sum of H , Al and Fe in

equivalents, was introduced as a factor determining the plant dry mat­

ter yield in cases that none of these reached the limiting toxicity

values.

In acid sulphate soils, rice responded favourably to rock phosphates.

Phosphorus is the main limiting macro-nutrient for crop production in

these soils, but the use of superphosphate is a luxury in many devel­

oping countries because of their limiting foreign exchange. Therefore,

the effectiveness of rock phosphates for lowland rice on acid sulphate

soils under various management practices was studied in pot experiments

on surface horizons of two acid sulphate soils under three application

methods and two rates. Details of this experiment is given in Chap­

ter 5. Rice response to phosphate sources varied between soil. In Mali-

nao, the highest rice yield was obtained when rock phosphate was ap­

plied and incubated three weeks before transplanting at field capacity.

205

In Chapter 6 a computer simulation model was developed to calculate the

time course of acidity production from pyrite oxidation in relation to

the changes of groundwater table, evaporation, entrance of oxygen and

different chemical reactions. The model is based on a multicompartment

model in which the soil profile is divided into a number of layers, is

written in CSMP and contains three main parts: INITIAL, DYNAMIC and

TERMINAL. For each compartment of a clay loam and a silty clay soil,

the compartment thickness, its water content, pyrite content, cation

exchange capacity, total cations, adsorbed cations and oxygen concen­

tration are given as inputs. Three evaporative demands of 4, 6 and

9 mm.d were used as a boundary condition at the soil surface. These

substantial differences in evaporative demand lead to increasing water-

loss. Results show that the oxidation process and the associated acidi­

fication of the soil are only marginally affected by the different

evaporative demands, although the oxidation rate was very much in­

fluenced during the early part of the evaporation process.

Results from this thesis shows that minimizing the oxidation of pyrite

by application of mulch during the dry season and maintaining higher

groundwater tables can avoid the acidic hazards. Research along this

line should be directed toward the feasible application of this package

to the field. In addition, other experiments should be carried out to

study the following:

varietal screening for short duration, acid-tolerant, salt-tolerant,

iron-tolerant cultivars;

- studies on fertilizer application should aim at optimizing the use

of phosphate, preferably rock phosphate;

- development of quantitative models to predict the effects of drain­

age at various depths, irrigation and other management practices on

the physical and chemical properties of acid sulphate soils.

In order to validate these models, basis data on physical and chemical

processes under various boundary conditions are needed.

CURRICULUM VITAE

The author was born in January 10, 1951 in Quang Nam, Da nang Province,

Viet Nam. He finished his high school in 1969 and graduated at the

National Agricultural Institute, Saigon as Agricultural Engineer (major

in Irrigation and Drainage) in 1973. Soon after his graduation, he ob­

tained a fellowship to persue further study at the University of the

Philippines at Los Banos. He gained a M.Sc. degree in Agricultural

Engineering (major in Irrigation and Drainage and minor in Soil Scien­

ces). In 1977 the author was sponsored by The Interim Mekong Committee,

the International Rice Research Institute and the Dutch technical

cooperation program to carry out his promotion work for the degree

of Doctor of Agricultural Sciences at Wageningen Agricultural Univers­

ity.